There are hundreds of parks. There will be space no matter when you come. Our park has a big influx right after Christmas, but until then there is plenty of space. The RGV is a big area that extends from Brownsville up past Mission and beyond. That is probably where the greatest concentration of RVers are. So there are several areas and the weather will vary a bit. So come on down and find a spot. . .rent for a few weeks and if you want something different, move on and explore the whole region.
Dale