ski-light above shower..

I had the same concern after I bought my camper a couple years ago. I dropped the inside plastic panel and and found a little wood rot and discoloration on the edges of the opening cut for the skylight. I thought for sure the leak was external, but I couldn't find the source.

What I determined was that there was NO seal on the inside panel which was allowing humidity from the shower to get trapped between the inside and outside panels. For a 10 year old trailer, the damage was very minor.

Rather than seal it off completely and risk it not being able to dry somewhere (which causes rot), I decided to coat the wood and foam with a thin layer of tub and tile caulk to help it repel the moisture. I left it unsealed from the inside to give the condensation a place to go.

So far I have not seen any further discoloration or indication more damage has occurred.

Take closer look at the roof. I had the same thing a few years ago and turned out water was getting under the roofing thru the radio antenna. You may have a small cut nearby from the branch that broke the outer cover. We had to replace the rubber because it was to late by the time we figured it out.