jec6613

That's super common actually.  Motorola repeaters are just a pair of their mobile radio boards in the same chassis, same for Yaesu being a pair of mobile boards, Wouxun's dedicated repeater, and so on.  It saves a ton on development and manufacturing costs.  The real enemy is heat, as you've noted.
What dedicated repeaters do differently is cool the boards better - larger heatsinks, ducted fans, and forced ventilation are common in a front to back 2U 2-post chassis normally used for repeaters, while the mobile radio usually must passively sink the heat, or, at best, has a low noise 40mm fan.  A 2U chassis can easily vent over 2kW of heat if designed properly (just look at servers), a couple of hundred watts for radios and control boards is basically nothing a single 60mm fan can't handle.  At least, once you stop caring about the audible noise of the cooling system!
If I were building a repeater on the cheap, personally I'd pick up something like this and take my tin snips to the interior: https://www.newegg.com/black-athena-power-rm-2u200h/p/N82E16811192310
It comes with two 12V fans, plenty of room for the power supply and the RX unit, in a couple of hours it could easily turn two independent mobile radios into a repeater.  I'd probably throw in a temperature sensor and fan failure alarm too for my own peace of mind.

That's super common actually.  Motorola repeaters are just a pair of their mobile radio boards in the same chassis, same for Yaesu being a pair of mobile boards, Wouxun's dedicated repeater, and so on.  It saves a ton on development and manufacturing costs.  The real enemy is heat, as you've noted.
What dedicated repeaters do differently is cool the boards better - larger heatsinks, ducted fans, and forced ventilation are common in a front to back 2U 2-post chassis normally used for repeaters, while the mobile radio usually must passively sink the heat, or, at best, has a low noise 40mm fan.  A 2U chassis can easily vent over 2kW of heat if designed properly (just look at servers), a couple of hundred watts for radios and control boards is basically nothing a single 60mm fan can't handle.  At least, once you stop caring about the audible noise of the cooling system!
If I were building a repeater on the cheap, personally I'd pick up something like this and take my tin snips to the interior: https://www.newegg.com/black-athena-power-rm-2u200h/p/N82E16811192310
It comes with two 12V fans, plenty of room for the power supply and the RX unit, in a couple of hours it could easily turn two independent mobile radios into a repeater.  I'd probably throw in a temperature sensor and fan failure alarm too for my own peace of mind.

Getting an antenna on the roof, 10 miles with 5 watts is quite reasonable even with the dinky little ones that come with Midland's "Micromobile".  Actually, in a pinch, throwing one of those on the lid of your gas grill does pretty good as well - just getting it outside of the home will help a lot.
As a rule of thumb, in GMRS in most situations, the extra height of getting it to the top of the roof will help range more than a lower-down higher performing antenna.  However, topography around you will impact that more than anything - for instance, anything bolted on to the backside of my home does as well as something on the roof because of my local topography - I can reach about 1 mile in one direction, and 50+ in the other so long as I have at least 10 watts.
Honestly, so long as you're within about 30-ish degrees of vertical, not worth it to bend the antenna.  Anything under 3dbi gain is going to be effectively an omnidirectional antenna anyway, and you're close enough to vertically polarized that you can talk to all of the other vertically polarized GMRS users no problem.
At most normal antenna sizes, the polarization will matter about as much as pure antenna gain.
Whatever you do, ground it correctly and get a good lightning arrestor - I use TMS personally.  Lightning strikes are no joke!
 
IMHO: If you have a gable, I'd run it discretely along or behind the facia board, and just drop an NMO mount into the center of the vent (maybe after making a flat area with a hammer) at the top of the roof, at about the same distance from the end as it is wide, seal it thoroughly to the roof, and then slather the connector with dielectric grease and put one of the little 2.1 db gain antennas.  I wouldn't even bother with a Laird Phantom, Midland Ghost, or similar, they're really great on vehicles, but on a structure, they don't perform much if any better than the 1/4 wave verticals that everybody gives you for basically free.  If I didn't have a gable, then I'd punch it down through the barrier into the attic, then seal it all up afterwards.

So, since this is the GMRS forums, which one of these are part 95 compliant?  Because, sometimes, it's not academic if they are or aren't.

So, since this is the GMRS forums, which one of these are part 95 compliant?  Because, sometimes, it's not academic if they are or aren't.

So, since this is the GMRS forums, which one of these are part 95 compliant?  Because, sometimes, it's not academic if they are or aren't.

So, since this is the GMRS forums, which one of these are part 95 compliant?  Because, sometimes, it's not academic if they are or aren't.

CTCSS is older and more prone to spurious noise opening the squelch - weather or ambient. Additionally, there are relatively few usable tones. DCS is newer was was designed to address those shortcomings.
 
Both came out of Motorola, who initially was one of the only manufacturers of radios with enough frequency stability to use DCS (though others caught up quickly). Even today, some Baofeng as they age have trouble with a DCS system. Also, many older radios can't use DCS at all, and a few transitional models needed modules to enable it (usually you'd swap our the CTCSS module to a dual mode module).
 
So, yes, DCS is better, but CTCSS more compatible.

You'll have access to the back catalog then. Every other issue or so there's an equipment review, and they're remarkable how comparable they are over 50+ years with consistent measurements.

There are plenty of good used quality brand name HTs on ebay at well under $50. BTW, it depends on which CCR you compare prices with. Right now on Amazon the lowest priced radios, 16 channel, no display, are at least $15. On ebay there are several Motorola P1225s listed starting $19. Though you might have to buy an antenna, battery and charger with the super low priced ones. You can easily get a working, ready to go, P1225 for under $40. OTOH, the P1225 is certified for GMRS. And, as far as I know, none of the really cheap CCRs are GMRS certified. Once you add certification, the CCR prices jump to over $50.
 
And keep in mind, GMRS certification is not just snob appeal. It actually means something. Sure, in some cases it just means the radio has limited front panel programming capabilities. But, in other cases, it means the radio is not complete shit.

For reference on how bad some are... The Wouxun 805G will set off my smoke detectors if used within 5 feet of them. 50W on 70cm with a Yaesu with an antenna hung next to the detector doesn't do that though.

All of this.  A UPS is great to bridge to an automatic standby generator, but that's about it.

Note that on an FM or Phase modulated radio all transmissions are analog. Digital data is actually represented by the presence or absence of an audible or sub-audible tone. IIRC 131.4hz is used for DCS. If the signal frequency is not stable, the DCS sub-tone will also vary, making detection of the bitstream difficult or impossible.

Have fun everybody ... https://www.timesmicrowave.com/calculator/
 
Also, there's insertion loss on each connector, which you can find in the spec sheet, not to mention any losses with poor assembly.
 
Oh, and if you're using UHF connectors like virtually all of the radios are, try re-seating the connector, because SO239/PL259 can't mate with enough consistency once you get to even VHF.  They're called UHF connectors because when they were invented, UHF was 3-30 MHz.

This is *exactly* why I have GMRS.  There's no way my XYL will get her ham ticket, so I needed something in between to communicate with her.
 
In fact, I have an HT programmed for her to have with her during inclement weather.  Three times this year, we've lost cell service at either home or her work (I WFH), and we've had major road closures and other problems - it starts listening to a small section of the upper 440 band, with a few, "Channels", and transmits on GMRS.  Why?  Because as a ham, I can put up a much more larger antenna and use a lot more than 50W of power to reach her and receive her signal.

"Cheap" is relative, the only true 2W (and not 1.2 or so) that I've found are the DeWalt ones, and they cost as much as a Wouxun GMRS setup - though they're much better built.

A loop is generally better for DF because it has a very even radiation pattern, slowly rolling off from peak in a predictable way, and is deaf only end-on - gain is slightly better than a simple dipole.  A rhombic has insane gain, but is extremely directional and basically deaf outside of its narrow forward lobe, and the secondary lobes off at 90 degrees to either side.  That of course makes it excellent for fixed installations, and its ability to fold up very small for UHF and upper VHF is another large benefit.
 
Rhombics fell out of favor mostly because of how large they need to be when set up - four sides of 1.5-2 wavelengths is pretty beefy even on the 2M band, and ideally half a wavelength above ground.  Not a problem for UHF, but big trouble once you start getting towards lower VHF, such as 6m, where each leg is 30 feet long at minimum, and about 10 feet off the ground, and for 160m HF you need 700 foot long sides and it to be about 270 feet in the air ... not ideal.  Once the transoceanic cables opened to replace the HF radio links, they've mostly been a forgotten technology - Yagis are slightly less gain, but you can turn them on a rotator, even for HF bands, and height above the ground is much less important.  Some amateur operators with enough space and finances still do use them though, since they can get around the world on the 20, 40, and 80 meter bands even when they're closed like they are now.

As a quick follow-up, a Rhombic for GMRS packs stupidly small, as small as those tacticool folding antennas. You just need about 4 yards of wire, an 800 Ohm resistor, 4 one foot long sticks, a bit of feed line, and the hard part: a 16:1 balun, and you have 16+ dBd gain, or over 18 dbi gain. 
Radiotelegraph and telephone services used to use them on HF for AM voice and CW, they provided a reliable link from LA to Shanghai, and London to Johannesburg, among other pairs.

You can still usually get out in an emergency, relying on a repeater as your only way out is usually a bad idea, anyway.  Interference aside, what about power outages or maintenance, both of which are much more common?  Put yourself on another channel, and use a bit of equipment to be prepared to try simplex on the traveler channel, or have somebody listening for you.  GMRS actually has significant power available to it, 50W on UHF can do crazy things put through the correct antenna.  Most, "Jammers," are using either CCR's or something like a Motorola Talkabout.  Protip: the cheap radios that aren't Part 95 certified are generally dumping half of their power out to harmonics, and they will spill over to adjacent channels, so watch for that and open your squelch to check for it.
 
First, set up a protocol to check back with someone back at civilization ... either you check in with them a few times/day and if not they send someone, or ask them to listen for your transmissions a few times/day, like the ham wilderness protocol.
 
And if you're counting on GMRS to get out in the event of an emergency, I highly recommend getting a GMRS tuned HT antenna at bare minimum.  I have yet to come across one that comes with a decent antenna, most of them might as well be dummy loads.  Nagoya 701G/777G at minimum, and just throw the rubber duck in your bag as a, "Just in case," antenna.  If you're using a HT the same as usual with a long GMRS tuned whip on it, you can expect a bit over 6 dB of gain (that's 4x the power pointed at the horizon) over your stock HT antenna ... if you use a speaker/mic and get the HT dead vertical and away from your face, about 8-9 dB if you use your body as a giant reflector.
 
And of course, with portable Yagis and collapsible Rhombics fed from 50W, you can go crazy and sling GMRS upwards of 100 miles.