I think this may be entirely doable within our lifetimes, but you're right, the demand won't be coming from the small off-the-grid RV community. It will come from the ongoing desire to extend a cell phone's battery beyond a day, or to give an electric car a range of 500+ miles. Google around for "battery breakthrough 2014" and you'll see many headlines about fancy new batteries that can have over 10,000 recharge cycles, or quadruple capacity, etc. but in reality most of these are years off from production. Additionally, the cost of batteries is simply too high, but even that's predicted to drop to below $100/kwh. Once we live in a world where the cost the electric battery in your Tesla is only $5,000, not $30,000, and capacity is 2-3x more, it would be conceivable to have a fully electric, solar-charged RV with, say, 5-6 Tesla car battery stacks. That will be a pretty sweet futuristic RV where you could literally never need to plug into shore power if you desired to stay off the grid indefinitely. You might not be able to drive more than 400 miles in a day, but hey that's alright.
Until then, diesel remains king!
