I understand the hesitance, but we’ve all seen hundreds of vehicles our entire lives that have permanent antenna mounts in their roofs. They look better than having a cable laying on the roof.
Why not get full enjoyment out of the truck for as long as you own it? It’s like suffering with cheap cupboards, worn out flooring, and an inefficient furnace for 30 years and then fixing up your house to sell it. None of the comments I’ve seen from people who sell or trade off vehicles with permanent NMO mounts make me think the value is affected.
I don’t know if you’ve looked into the Bulletproof Diesel third brake like mounts, but that might be another option. Finally, there’s a company that makes replacements for the factory GPS or satellite roof mount antenna that provide an additional two way radio mount. If you’re interested I’ll see if I can find them again. I’m not certain what models they cover.
I would compare the strength of self adhesive steel disk trick on top of the roof to the large magnet under the roof liner. I’m not certain that two magnets on either side of an aluminum roof will have as much attraction. Try both methods and let us know, please.