Jones

If you can afford it, use the LDF4-50A.  Perhaps even LDF5-50A if your run is longer than 100 feet.
 
At 460MHz at 100 feet, RG-8x has a loss of 9.4 dB. LMR 400 has a loss of 2.7 dB. LDF4 has a loss of 1.4 dB. LDF5 has a loss of 0.82 dB.
 
If you are using LDF Heliax, it is just fine to use a short jumper at the end for flexibility going into your radio.
 
Also, keep in mind your cost vs. return on investment ratio.  How far do you really need to talk?
 
Personally, I use LDF4-50A, but I'm only running about 80 feet.

For thought...if you need to run that much coax, it would be worth it to buy something like a Motorola Desktrac with tone remote capability. Mount the radio in the attic or silo and run a short coax to the antenna, then a CAT5 from the radio to a tone remote. Now you have Base Station! 

If you are planning on eventually running 100 feet, you WILL need better coax cable.  RG-8x is NOT RG-8u.  8x is the small coax used for CB radio.  Even the best grade of 8x has over 9 dB of loss at 462MHz at 100 feet.  For the low-cost/best performance per dollar ratio, go with LMR-400.
 
NOTE: I do not EVER recommend LMR-400 for repeater use, but for simple base station operation, it works great.

If you can afford it, use the LDF4-50A.  Perhaps even LDF5-50A if your run is longer than 100 feet.
 
At 460MHz at 100 feet, RG-8x has a loss of 9.4 dB. LMR 400 has a loss of 2.7 dB. LDF4 has a loss of 1.4 dB. LDF5 has a loss of 0.82 dB.
 
If you are using LDF Heliax, it is just fine to use a short jumper at the end for flexibility going into your radio.
 
Also, keep in mind your cost vs. return on investment ratio.  How far do you really need to talk?
 
Personally, I use LDF4-50A, but I'm only running about 80 feet.

If you are planning on eventually running 100 feet, you WILL need better coax cable.  RG-8x is NOT RG-8u.  8x is the small coax used for CB radio.  Even the best grade of 8x has over 9 dB of loss at 462MHz at 100 feet.  For the low-cost/best performance per dollar ratio, go with LMR-400.
 
NOTE: I do not EVER recommend LMR-400 for repeater use, but for simple base station operation, it works great.

I think you may be confusing a drip loop for a common-mode choke.
 
If you have a proper antenna, with a true unbalanced feed point, you do not need a choke at the antenna.  Those are only required if you have one of those cheap ham-type J-poles, or other balanced feed antenna.
 
If you do need a choke on your antenna, do NOT make it by coiling 1/2" line.  Leave the 1/2" straight up to the base of the antenna, and use a 3-foot jumper of RG-8x, RG-58u, or similar small coax to make your coil, which should be 4 or 5 turns about 6 inches in diameter.  You can also make a common mode choke by taking a foot-long jumper of RG-213 or LMR-400 and put ferrite clamp-on chokes all the way from one end to the other.  Again, on most decent commercial antennas, this is not needed.
 
A drip-loop is simply a low-point in the coax right before it comes into your building, so that rain running down the coax will drip off onto the ground, rather than get funneled into your house. This is not even needed in all installations, as sometimes the coax is not running down a tower, but rather across a roof, under a soffit, or into a conduit.
 
Short jumpers at each end aren't going to hurt you much. As Lscott posted, use type "N" connectors where-ever possible for lowest loss.

I think you may be confusing a drip loop for a common-mode choke.
 
If you have a proper antenna, with a true unbalanced feed point, you do not need a choke at the antenna.  Those are only required if you have one of those cheap ham-type J-poles, or other balanced feed antenna.
 
If you do need a choke on your antenna, do NOT make it by coiling 1/2" line.  Leave the 1/2" straight up to the base of the antenna, and use a 3-foot jumper of RG-8x, RG-58u, or similar small coax to make your coil, which should be 4 or 5 turns about 6 inches in diameter.  You can also make a common mode choke by taking a foot-long jumper of RG-213 or LMR-400 and put ferrite clamp-on chokes all the way from one end to the other.  Again, on most decent commercial antennas, this is not needed.
 
A drip-loop is simply a low-point in the coax right before it comes into your building, so that rain running down the coax will drip off onto the ground, rather than get funneled into your house. This is not even needed in all installations, as sometimes the coax is not running down a tower, but rather across a roof, under a soffit, or into a conduit.
 
Short jumpers at each end aren't going to hurt you much. As Lscott posted, use type "N" connectors where-ever possible for lowest loss.

I've spent decades in emergency services. If I worry, then you should worry. Right now, I'm more concerned about the idiots that are causing chaos and panic by over-buying food, water and TP.

If you can't hear the repeater on the regular 675 channel, then you must be running tone squelch, or "Private Code" on that channel that is not the same tone as the repeater.  ...otherwise you would hear it.  675 is 462.675 on receive whether you are on repeat mode or not. 
 
That is exactly what tone squelch is for... so you DON'T hear anything but other radios with your selected tone.

I don't have a GMRSV1, but if it is like other Btech rigs with CHIRP, then you would select 'TONE' for transmit tone only, and if you want tone on receive as well, then you would select 'TONESQ' which will allow you to set both tones separately.
 
If you want to receive everything, there is never a need to set a receive tone on your radio.

https://www.bridgecomsystems.com/pages/bridgecom-systems-spring-repeater-system-giveaway?gsr=Ls2KI-8ahVWZ8spi

I read the specs on the Tera, and what I've found is the thing is set up by default to scan when on channel 16. It is likely that it is in scan mode, and when you transmit, it will stop on whatever channel it was last going past.  If you key up the Midland first, the Tera will stop on the frequency it hears, and stay there for a few seconds, thus you can then transmit back to the Midland. 
 
The frequency chart for the Tera does not line up with the Midland.  Channels 1-7 will be the same, but on the Tera, when on channel 8 or above, you need to add 7 to the channel number to match the Midland.  In other words, if the Tera is set to Channel 11, you will be on 462.625, which is channel 18 on the Midland.  If you are trying to use channel 16 on the Midland, then set the Tera to channel 9, and you should be able to talk.

I read the specs on the Tera, and what I've found is the thing is set up by default to scan when on channel 16. It is likely that it is in scan mode, and when you transmit, it will stop on whatever channel it was last going past.  If you key up the Midland first, the Tera will stop on the frequency it hears, and stay there for a few seconds, thus you can then transmit back to the Midland. 
 
The frequency chart for the Tera does not line up with the Midland.  Channels 1-7 will be the same, but on the Tera, when on channel 8 or above, you need to add 7 to the channel number to match the Midland.  In other words, if the Tera is set to Channel 11, you will be on 462.625, which is channel 18 on the Midland.  If you are trying to use channel 16 on the Midland, then set the Tera to channel 9, and you should be able to talk.

Possible problem #1 - units too close together. solution: they won't work in the same room with each other due to overload. Move them apart by 100 feet or more.
 
Possible problem #2 - CTCSS or DCS settings do not match. - "Private Codes" are NOT the same number on each unit. Solution: Get a chart for each unit, and set them for the same CTCSS frequency or the same DCS code - watch for normal or inverted codes.
 
Possible problem #3 - Tera unit on charger, using speaker-mic to make a "pretend" base station. - Solution: Take it off from the charger base.  The thing is meant to run on its battery.  It WON'T transmit properly while sitting in the charger stand, and will transmit a loud 120 Hz buzz, if it transmits at all.

Comic relief break:
 
"My wife said she was going to leave me unless I quit spending so much time on the radio.   ...OVER"

Comic relief break:
 
"My wife said she was going to leave me unless I quit spending so much time on the radio.   ...OVER"

I came across a short (under 4 min) professionally made video showing how citizens in fire prone areas took action to have some kind of communication network. This came about because of the horrific fires in rural areas and loss of telephone and cellphones. 
 
https://www.youtube.com/watch?v=2uhOwng_j38
 
The solution was to purchase GMRS radios and apparently quite a few where sold in just one rural area. They had some help from what looks like a ham or two (but did not identify them as such), and even set up a modest repeater to get across one ridge area. The equipment shown were Midland MXT series radios. And for this application, I think this is a good choice for plug and play. 
 
 

Read your own words. If the intent of your transmission is to interfere with the communications of another station, it is prohibited.  And, no, the rules do not limit that to properly licensed stations and for good reason. If they allowed you to interfere with improperly licensed stations they would be granting you the power to not only accuse, but also judge and then punish others for violating the rules. That job is reserved for the FCC.
 
However, the rules do give you a way to deal with improper use of the airwaves, If you think someone is violating the rules, then you can report it to the FCC. 

Not even in jest.
 
§ 95.333 Prohibited uses.
No person shall use a Personal Radio Service station:
[... ...]
(d) To intentionally interfere with the communications of another station;
[... ...]

Forget all of that bulkhead connector stuff.  That is a problem waiting to happen.  If the cab ever has to come off, just replace the whole mount if needed. That would be cheaper than all of the added connectors for that bulkhead setup, and those connectors ARE lossy.
 
Here's another better idea... just drill a hole in the top center of the cab roof, and mount the antenna there.  If the cab ever needs to come off, the antenna comes with it.  You will also get better results with the antenna on the roof than you would with it on the rack due to a more evenly distributed ground plane around the base of the antenna.

Still no wideband.  Still no split tones.  I don't expect that to change anytime soon.
 
Just an assumption on my part, but I think the target market for their GMRS products are non-tech people who want an OTC product that works out of the box with no special knowledge or prep.

My major concern with the idea of using a bulkhead connector on the outside is it would be nearly impossible to weatherproof adequately.

The OP said he wanted to be lawful.  The MARS/CAP mods for ham radios are not in any way legal to use on GMRS/MURS.  Those mods are only legal if you are in fact a member of the Military Affiliated Radio Service or the Civil Air Patrol, using the radio on the military frequencies just outside of the ham bands.

Forget all of that bulkhead connector stuff.  That is a problem waiting to happen.  If the cab ever has to come off, just replace the whole mount if needed. That would be cheaper than all of the added connectors for that bulkhead setup, and those connectors ARE lossy.
 
Here's another better idea... just drill a hole in the top center of the cab roof, and mount the antenna there.  If the cab ever needs to come off, the antenna comes with it.  You will also get better results with the antenna on the roof than you would with it on the rack due to a more evenly distributed ground plane around the base of the antenna.

Forget all of that bulkhead connector stuff.  That is a problem waiting to happen.  If the cab ever has to come off, just replace the whole mount if needed. That would be cheaper than all of the added connectors for that bulkhead setup, and those connectors ARE lossy.
 
Here's another better idea... just drill a hole in the top center of the cab roof, and mount the antenna there.  If the cab ever needs to come off, the antenna comes with it.  You will also get better results with the antenna on the roof than you would with it on the rack due to a more evenly distributed ground plane around the base of the antenna.