I found a leak in my old campers cab over. I was able to remove the screw strip and found a 2" area about three feet long. Mine was wood framed and I was able to peel back the side covering and cut out the bad wood I then glued and screwed a strip of yellow wood and coated everything with fiberglass reason. I let that dry and filled the void in the foam insulation with spray foam and covered the whole thing with fiberglass.The whole job took about 6-7 hours and made a very good repair. Granted I must have caught this early because there was no sign of interior damage.It looked like mine also started in the upper edge of where the cab over curves under.I think the outer cover was cut short at the factory letting water in after the butyl tape shrunk over time.
