There are many people who RV on limited incomes like social security and pensions. Of course, everyone does not get the same amount of social security benefits or pensions, so it would be important to make a budget of estimated income and expenses before setting out. When you are able to purchase your RV with your savings, it is easier because then you can set aside some of your income for emergencies such as medical problems or repairs on the RV.
On a limited income, you would have an easier time RVing in places where you could get free or very reduced fees on campgrounds, i.e., National Forests, Corps of Engineers campgrounds, BLM, and other public lands.
In the years when we lived in our RV full time, our biggest expense was gas as we liked to move around a lot. When we camped in the southwest, we did a lot of boondocking, so camping fees were very low. The times we traveled to the southeast and eastern states, camping fees were much higher, though we were able to find some nice National Forest campgrounds.
Living frugally becomes a way of life for many retirees who live in their RVs.