When we bought our old 1995 Coachmen, it was missing the left rear wheel opening trim. Since both sides were interchangeable, I used the right one to make a duplicate formed from thin aluminum flashing. When it fit to my satisfaction, I filled the back side with spray foam trimmed flush and painted it to match the other side. The right one had a couple of cracks in it, so I heat welded them closed from the back side, and filled that one with foam too.