I have read various things about this, from extremely successful to the truck bed compounds cracking, splitting, and causing untraceable leaks. I've been following this for a few years now because there are a few promising things that I've seen. Both Dave's Permanent Coatings and Rhino Liner offer epoxy elastomer spray-on applications... but you have to drive to Florida for rvroof.com, and Rhino Liner only has a very few shops... for me, it would be a 500+ mile drive.
If some company like Line-X could get this available in most major cities, they would have a bonanza on their hands, just because it would pretty much cure the #1 cause of RV destruction out there... water damage.