I know some of the Protonex guys and have seen their system. It's pretty cool, and they do a decent fuel cell. But remember.... it is still a fuel cell. These things don't work forever; you get a certain number of hours and then you're going to replace your stack, which isn't cheap. And note, these suckers are pricey!
Another option that I think may have better applicability to RVers is the propane-based fuel cell system from Adaptive Materials. See: www.adaptivematerials.com
Runs off propane, so your fuel source is a lot easier for most. But again, you get something like 200 hours of runtime, and then your efficiency is probably starting to degrade. And the stacks are pricey. Then again, anyone with a SMB might have that kind of money... I'm thinking the yacht group is a better target for early fuel cells...