had a similar problem. I found water on the rear dinette table top, and on the rear seat cushions. I thought the water was coming from a cracked corner of the overhead Fantastic fan curb. I caulked it and still had moisture intrusion after the next rain a few months later. I read about the scupper problem here on the forums and rodded them out. after rodding the scuppers it still leaked. I then suspected the caulking holding the window frame in place was the culprit, and proceeded to remove the rear window. It was solidly caulked to the trailer shell and there was no way it was leaking, so I re-installed the window screws and was back to the beginning again. I then did some hose tests and discovered the leak was indeed coming in via the lower window track caused by clogged scuppers! I then removed the screens and slid the window open fully. I then discovered the lower window track liner could be removed from the aluminum window frame. Mine were completely mucked and mired with black gunk. The previous owner must have parked the trailer under some really messy trees or ?. After much hydro jetting with the hose nozzle the scuppers were running freely and clear. There was no way merely rodding with weed whacker cord would have cleared my scuppers, as it just pushed the muck back into the track. After cleaning you can re-test with the hose and verify your work. I ended up doing all the windows
on my trailer and spent less than an hour to do all.
If your water is entering higher on the trailer, I would check all the roof penetrations such as vents, ac, rivets, wire penetrations, etc, by doing a hose test. Always start the test at the lowest elevations first and work your way up. Have a helper inside feeling and looking for intrusion. Spend a few minutes at each elevation before working higher to give slow leaks
a chance to show. Walkie talkies or cell phones are good to communicate with your helper to describe where you are applying the water.
Never neglect a leak, as they will cause many more hours to repair the damage as the hours to detect and seal.