Good question. my thought is the price of fuel has pretty well killed the idea of going mobile for retirement for a lot of people. Space rent for RVs isn't cheap either. Between the two, I think it's cheaper to fly where you're going and rent a room when you get there.
Mobility means selling off most non-essential belongings for many people. No room for more than one or two machines in an RV. Someone is bound to tell me they're in an RV and have 20 of them but still in general most mobile people don't have extensive collections of anything with any size at all to them.
We have a very limited budget. Even at the somewhat lower $3.00 per gallon here at the moment I do take the cost of fuel into consideration. It can easily make a good deal into an expensive machine. Shipping is high these days too.
Rodney