Gordon, I mainly use .040 for the sides and 080 for the roof panel. Since the inside is not visible, I use a piece of angle inside each corner. It gives you a little more meat in order to round the outside corners off. It makes the sleeper a little heavy, on a long w/b truck I use a thin piece of aluminum as long as possible super glued inside the frame rails. Keeps the frame from sagging over time. My models are in an office in a metal building , tends to get hot in the summer. I've found that the thicker roof keeps it from sucking inward. Once again, shelf models-no shows, so inside detail is not as important. Thanks to all for looking!