If you look at where the Ford/Chevy cab ends and the fiberglass coach body begins this is the seam area. In my case, a Thor Chateau 31A bunkhouse, the rubber roof meets up to the fiberglass cap. There is lap sealant covering the trim. The edges have a plastic molding running down the fiberglass cap. Here's what to check.
1. The lap sealant has no holes or bubbles and extends beyond the seam in the front and back of the trim.
2. The running lights have silicone sealant around them. (Mine had gaps and holes in the sealant and the running light lens cover gasket was no existent). I fixed them and checked them by washing them and observing that no moisture formed on the inside of the lens.
3. A good bead of silicone sealant is around the top and side window frame of the overhead window.
4. A good bead of silicone sealant round the trim of the fiberglass front cap.
I live in AZ so the sun does more damage than water. But it does rain occasionally. So proper maintenance and inspection will always be required.
