To the OP....If I was on a limited fixed income(SS), I would do exactly as you are contemplating, instead of throwing money into someone else's apartment and not being able to afford to go anywhere.
Get a nice gas rig(doesn't need to be all that new)just mechanically sound. One or two slides should be plenty for one person. I'm going to use $1500 a month as an example. If you pay $300 a month for a payment,$300 a month for food(I do that), that gives you $900 a month for fuel and repairs(if needed).
The real criteria for what you are suggesting is to travel in moderate climates where you don't need to use the furnace or ac much. I would suggest leaving your area in the fall and being in AZ during the winter. In the Quartzsite area(and a few other places)you can stay on BLM land for several months for about $60 a season. That alone should let you save some money for unexpected expenses.
There are also many forest service cg's, DNR cg's, etc. that you can stay at for free or a minimal fee.
I could give you lots more suggestions for living and traveling on a limited income, as it is feasible to do what you are planning to do. You won't be living the life of luxury, but you can certainly see and enjoy our country if you stay away from the populated expensive areas.
I forgot to mention that staying in BLM areas like Quartzsite in the winter, you will have many neighbors that would be more than happy to help you do any repairs or maintenance that you need done. Usually the guys are looking for an activity or project to keep them busy:)