Roof sealer, siding, and windows

#1
[Kenny Mc] I just bought a 87 Coachman class C, looking for a good inexpensive sealer to go over all the roof joints to make sure they do not leak. Is it a good idea to caulk around the windows on the outside to make sure they are sealed? And finally one side of the outer fiberglass is coming loose from the wooden frame and buckling, can I inject some liquid nails adhesive and glue it back? Thanks in advance for your suggestions.
 
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