We went from Fort Worth to the Keys this past summer. Our first night we stopped at a casino in Vicksburg. Extremely friendly staff. I had an electrical problem with my Travel Trailer so they let me change from my 30 amp site to a 50 amp (though that didn't actually resolve the issue). Offered any other assistance that they could provide as well.
There is a shuttle to the casino. The office is open 24/7 with a TV and showers, etc. Not many trees or anything, but it is still a clean nice place to stay overnight. Inexpensive as well. I don't remember the exact price but it was in the $20's and I think the 50 amp site was only a couple of dollars more even though she didn't charge me the higher rate.
Ameristar RV ParkAmeristar Casino