When I was looking for a truck camper a couple of years ago, I looked at many many campers, of those campers there was a fair share that were advertised as remodeled. Basically they painted the interior. The reasons for the remodel im sure was varied, but none of them (as in absolutely NONE) were as nice or clean looking as the original finishings. I came to the conclusion that repainting was a whole heck of lot of work to do it right. I would rethink the idea of painting etc. and try to make your jail cell more livable in ways that don't require a complete paint job. I am sure it can be done, and as mentioned above they were talking professional interior painters, if you insist on painting Id go in with idea that painting even a truck camper is more than slapping some paint on the walls. You asked for ideas, concerns in painting the interior of your truck camper, I say don't do it.