How to determine material used on sidewalls of my 5th Wheel

Gel Coat is a smooth color layer that is sprayed into the mold first. Next comes the fiber glass. Filon mentioned by Scott is fiberglass. To tell if you just have filon..... look carefully at the walls. If you see fibers then you have filon....... no fibers and a smooth surface then it is gel coat or even could be paint.

Filon is least expensive, then gel coat then paint. Full body paint will only be on high end units.