My parents used to have an RV built on a freightliner chassis. While not a perfect example, it used ~6MPG in cities, and ~11MPG on highways (where it was driven 99% of the time). Also it was from 2004.
With all the things you find in an RV - Pop-outs, fridge, washing machine, etc, I would be amazed if it didn't weigh something similar, if not more than a city bus and at least equal to a inter-city bus.
Worst case scenario and all buses are driving around with 2004 level mileage, that is still only roughly 10x more fuel than the best mileage vehicles available today.
With all the things you find in an RV - Pop-outs, fridge, washing machine, etc, I would be amazed if it didn't weigh something similar, if not more than a city bus and at least equal to a inter-city bus.
Worst case scenario and all buses are driving around with 2004 level mileage, that is still only roughly 10x more fuel than the best mileage vehicles available today.
Smells like bullshit to me.