Try washing it first, you might be surprised. My trailer is a 1998 Nash. It has NEVER been covered. I park it under a pine tree in the back yard, probably the worst thing for it. My roof is fine. I just recently put Eternabond tape on the seams. Roof was filthy, I used Eternabond prep cleaner and scrubbed off all the dirt and it was bright white again.
If you think you need a new roof, I would strongly encourage you to research "Liquid Roof". I had a tear in the roof when I bought it used. I cut out the old rubber, fixed the rotted wood and used Liquid Roof to patch the hole. It is liquid EPDM rubber. It bonded to the old roof and made it back to a single piece of rubber. No leaks. Cost me less than $75 in parts and about an hour to prep and paint it on.
A couple gallons will be less than $250 (guestimate) and are easy enough to install yourself. Its messy, but it forms a 100% EPDM roof on top of your current roof.