I would throughly clean all the seams and around all roof penetrations. Then I would apply Eternabond tape to every one of those places. That should take care of all the roof leaks. Next, I would remove and re-caulk all the clearance lights around the top and sides of the trailer. I would also check all windows for good caulking and re-do if necessary.
If, after all this work, the roof still has a problem (not very likely) then I would apply the Liquid Roof product
right over the whole roof. .
Barney