To me, a battery pack and motor(s) with sufficient energy density to run the coach 350 miles at highway speeds at the same weight as the current driveline including fuel and tanks is the requirement. Charge it up overnight at the campground and go again tomorrow. Energy density isn't there yet, but the stuff like JimK mentions is moving in the right direction. Since we already have the (upgradeable to keep it in the pipe)infrastructure, I think the end game is hydrogen fuelling and fuel cells. Couple thousand square feet of solar cells running all day cracking water and storing the hydrogen for the vehicle. The tech exists now, sorting it to compete in price is going to take some doing.

--johnny