HighDesertStranger, I mentioned originally that our truck had been used as a mobile radiology lab and had a rather stark and sterile look to it. The original wall covering was luan plywood with the bonded vinyl covering for the walls and padded vinyl for the ceiling. As there was a lot of water damage from leaks, I stripped everything to the outside FRP and started from scratch. I first sealed all the potential leaks and seams both inside and out and then did it all a second time just to be certain. I used 2 inches of Styrofoam in the walls and 6 in the ceiling and everything is held together with both screws and also construction adhesive. I covered it all with luan and then that with padded vinyl which I got online from a company specializing in doing upscale boat interiors. The foam backing on the vinyl is 1/4 inch and this is held up with spray adhesive and the seams are covered with wood strips to hide the cut edge. I also used push in type fasteners similar to what is used in automotive interiors and even was able to create a nice diamond tufted motif on the ceiling with very little additional effort. This is really a bit more info than you were asking about but what I've ended up with is well worth the extra effort that I'm putting into it. I'm now in the process of installing the cherry cabinets and granite counter tops along with the appliances and I'll be done.
1999 Freightliner FL70 with Renegade Conversion, Cat 300 hp Allison 6 speed automatic