http://www.eternabond.com/Professional-Roof-Repair-Products-s/21.htm I would look close to this product for a permanent fix for one or several holes in the roof before spending thousands...unless your just wanting a new roof.
Also let google (rv roof repair/etc) be your friend for showing how the pros do it.
Be sure and follow Eternabond exact instructions....not some rv owner who's only experience is his one rv job.
Eternabond when installed per instructions and seal the edges with self leveling Dicor will last as long as the roof membrane.