Not sure what part of South Texas you are referring to, but I stayed for a fantastic 8 months on the Mexican border in Brownsville. There is a 4 star (Frommer's RV Guide) RV resort there called River Bend on Military Highway. I can't recommend it highly enough if you want all the modern conveniences, including an 18 hole golf course, heated pool and tons of amenities. I didn't want to leave there. They have some rental lots, but most are owned privately although a lot of owners will rent to people.
Call them on (956)548-0191. You will have a great time and you will be only 5 mins from Mexico as well!