Depending on how SOFT things are up there you might want to just seal it up and run...if you got a 50' roll of Eternabond tape you could just go right over all the seams....be sure to roll over the job with a small roller...by the time you get into the time and expense of the repair, you might exceed the cost of the trailer....Just. Thought...I bet 75% of the older trailers out there have soft spots on the roof...the main thing with the eternabond tape is the prep,,,,clean the surface well, let it dry, and roll right over it....