I'm a full-timer in a fifth wheel and I live on about that much every month, but I boondock most of the time because that's what I enjoy the most. I don't really try to save money I just do whatever makes me happy so I'm pretty sure you could live on $2500 a month and have enough left over to live in an RV Park, especially if you rent by the year, that's almost always cheaper than monthly.
I spend my winters boondocking around southern Arizona and I see lots and lots of RV parks full of retirees so you will have a lot of choices. But if you get deep into southern Arizona you'll find a lot of those folks get out of there in the summer, it's indescribably hot, and your electric bill to run your air conditioner will be outrageous. If you look through my blog at theboondork.com you will find during the winter I often post my monthly expenses which might give you some idea what it cost to live in an RV.
theboondork.com