I used this stuff on my old class C:
http://www.epdmcoatings.com/rv_roof_repair.html
and it was great! Easy to use. Rolls on like thick honey and dries to a completely sealed rubber roof. This is the EPDM stuff that the RV roofs are made from too.
Cost me about 300 bucks for a 33 foot roof, took about 4 hours total.
Looks like a brand new roof when you're done. Just like painting, but very thick.
In fact, if you go to the site, and look under photos section, you can see many RV's before and after. Mine is the one in front of the barn with the X, and you can see, the old roof was just shot.
When I was done, a brand new roof, and a 5 year warranty.
anthony