I think I have the oldest so far:
1976 Dodge RV 18 foot Cobra towing a 20 foot Haulmark. Yep about 6-7mpg...or would that be gpm. But I do have the only wind powered RV that I have seen so far. It has a 400W wind turbine that I mount on a 20+ foot pole that hooks up to the batts on the RV.