Thanks for the contacts and advice. I have replaced flooring, torn out plumbing refurbed the inside of a few campers but now I don't have the time and if I am going to redo a roof I want it done right.. I appreciate the help..
A 'proper' roof replacement (if EPDM rubber) entails tearing off the old roof membrane, replacing any rotted/wet/molded underlayment (can involve wooden roof bows). Then mastic is applied and new roof material rolled out. After the adhesive has set the extra material is trimmed back and the metal trim on the sides and ends are reinstalled.
All roof vents, A/C units, skylights and plumbing vents will be installed and sealed.
This provides a 'seamless' roof save for the juncture of the rubber roof and both ends of the trailer.
IF you clean and treat the roof annually with a UV protectant (about $60.00 kit) your new roof should last 12-15 yrs. even if exposed to the sun.
Of course, you need to determine the value of the trailer and if your application (never moves, on a deer lease, etc) warrants the expense.
Whatever you choose to do....of prime importance, is to be certain you do NOT cover up any rotting wood. It will continue to spread.