There is a product to use on rotting wood, stops the process and turns it into a rock-hard piece of something with this stuff penetrated into it...Lowe's or HD. Might help your fix. Fixing the leak would be #1. If you plan to keep the trailer for any length of time, suggest you do the job completely. If you're going to unload it in the near future, possibly enough to get through this, advise the potential buyers and hope for the best.
Water is sure the enemy for RVs....regular built homes as well. Recently house shopping in FL and found a dandy buy on a cute place that needed "TLC". Loved everything until I got to the bathroom. Water damage around the skylight. I told DH to forget this and when he came in and saw it, we ran. Our current house had 2 skylights in the sunroom when we purchased it. Within a couple of years we were seeing the tell-tale signs. All the caulk in town wouldn't fix it, so DH ended up ripping off the ceiling, part of the roof around each skylight, tossed the skylights and replaced the whole thing with solid roof and solid roofing that matched our architectural shingles. Problem solved. I love the look of skylights but they are just a problem waiting to happen.
