This is a common problem.? Some have had the interior roof skin fall off while towing and splat down on the bed.??
The most likely way the water gets into the roof is the seal between the metal roof edge and the panel leaks, and then water gets inside, and flows along the bare roof panel edge for up to 12 feet.? Then it exits through the lower corner, and at least in Chalets, flows outside the trailer so the owner is probably not aware of the leak.
The best way to fix a waterlogged roof is to replace the roof panels.? You may as well replace the skylights and vents at the same time since those only last about 10 years before they get cloudy and/or crack. Plus removing skylights on some trailers breaks them. But you can reuse the aluminum roof edges.
That's expensive, though, so some have patched roofs in places that are rotted.? Its hard to get the new pieces of roof skin under the roof edges when you do that, however, so the repaired roof may not be as strong as the original.
I'm very surprised that a dealer was able to dry out a roof after drilling some holes.? There's a sheet of something on the inside of my roof that looks like it's waterproof.? I think it would take years for a saturated roof like mine to dry through some holes in the panel, if it ever dried at all.
