Thanks for looking and your comments. There is a large plastics company here in Phoenix. I can get the name if you want it. It is PVC. Exact specs I don't recall, but it's called 1/8 inch. Has a pebbled texture on one side and smooth the other. Quite expensive. $55 per 4x8 sheet in white. Black is a little cheaper. Problem was, the dimensions of the burb panels were such that it took 4 sheets to complete the project with considerable waste.
I was able to do the side panels under the windows and have more for the door panels and then some. As far as heating... we tried that on the rear panel. More waste... It has so many compound curves we tried everything to get it to fit. Heat gun did soften it but couldn't get enough area heated to have time to install it. (cooled too fast) Heated it more and it GREW. (warped badly) Very ugly and costly experience. Also it isn't as flexible as the cardboard liner so you can't make your pattern out of poster paper and expect it to fit the bow radius. I put this job off for a long time, knowing it was going to be a PITA. And it was. Sitting inside that car, neck crained looking up, large pieces of material, etc. My son was very gracious helping me complete it. It does take 4 hands at least. But I'm happy with the outcome. I may need to put a couple of white screws with the cupped washers into the ribs between the ones with the arched bows if it looks like it might sag or rattle. We'll see.
Richard
