OK, just one more post on RV and I will not sidetrack this thread further.
Do you really want something that old? I have seen plenty of RVs with less age and mileage and with asking prices of less than what people would pay for a new average car. I bought mine with 25K miles, and have not needed to do anything with the engine, other than to change oil. It's up to 45K miles now. The house portion needed some maintenance, but nothing serious.
So, you pay perhaps $20K for a vehicle that you live in for a few years, and if you send it to the junk yard afterwards, it is still not that expensive in exchange for the travel and life experience that it provides. And regarding fuel costs, full-timers usually linger for longer at each stop, so 500 mi/month sounds reasonable.
I use mine for traveling, so cover a few thousand miles in a month easily. It is fun. I am thinking about taking a 2 or perhaps even 3-month-long trip, covering 9K+ miles in late summer/fall this year.