We spent the month of Oct taking a look at RGV for the upcoming winter (Jan-Apr). Weather charts shows average Jan temp to be at least 10 degress warmer than Galveston. I'm amazed at the number of parks in RGV. You can barely drive 5 minutes without stumbling over one. Using Camppground Reviews and filtering only ratings above 7.0 we narrowed it down to a dozen or so. We settled on Canyon Lake and they were having a 4 for 3 sale (pay for 3, get 4 months). Brought the price down to 350ish.
On a side note, when we left RGV, we stopped at Magnolia Beach (slightly north of Corpus) for a few nights. Magnolia is rather famous for free beachfront camping. Camped a few feet from the water, it was special. Due to it being November, crowds were minimal. Also, no hookups, but for a couple of nights, it was terrific.