Worst I've ever done makin flat door panels, (but it came out pretty), was make fiberglass door panels (on a Nissan pickup truck). Lay out some plastic onna garage floor, and then lay out a single fleece blanket. Soak it good with fiberglass resin (about 1/2 of a gallon worked for me)... Keep it flat... then let it set up. Cut to size... on the one I did, it had to have a curved top, so after I cut it, I layed the flat piece edge-on on top of a 3 inch PVC pipe with plastic over it... More fleece and resin, and cut to fit. covered the whole thing in vinyl and it looked great!