Living full time in an RV can be as cheep or as expensive as you want to make it. On the cheep, stay for a month at a time(lowest rates) Camp host(free space and utilities). So your only expenses are food, propane, and fuel for your RV, plus insurance and medical. Expensive, resorts can run 50 or more dollars a day plus electricity. Eating out a lot of the time can be very costly. It can be what you want.
As for long term rentals? While that can become very expensive it is still far cheaper than buying one and discover you really hate the life and sell out at a hugh loss.