Sounds like a roof leak. Typically roof leaks start at bad caulk joints at the roof penetrations. First, do a visual inspection of all the caulk joints. Be careful getting on the roof. Depending how bad the leak is, the wood may have started rotting and you could fall through.
The caulking could also fail at the transition between the roof and the wall.
Another option is to take it to your local dealer and have them do a positive air test. They would install a blower to one of the skylights and blow air into the unit. Them they check all the joints by applying soapy water to them. If bubbles form, there is a leak.
If you are handy, you can do the repairs yourself. If not bite the bullet and pay the dealer. Either way, the roof leak should be stopped and the mold cleaned up to preserve the usefulness of the trailer.
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