There are various places to camp along the highway. Some may be accessible to RVs but I understand the road becomes very steep in spots. (We went about halfway.) Campgrounds are all primitive but there are some nice locations. Some have primitive toilets. We did not go into the “center” of the park since we wanted to stay on better roads. Overall, the area is beautiful in the winter.
Big Bend Ranch State Ranch is quite different than Big Bend National Park. While much of the national park has sky islands (mountains), much of the state park is classic desert. The park stretches from the desert to the Rio Grande River. There is a scenic road that runs along the river with a number of campsites. The campsite are drive up campsites, but somewhat primitive in nature in that there are not restrooms with toilets, sinks and showers. There are picnic tables and fire rings, but that is about it. There is not much shade cover at these campsites so it is helpful if you have a tent or canopy shade. The attraction of this park is the expansive views of the desert that one is able to view. The heat and lack of cover can be tough on the body, so bring lots of water and hydrate. Outside the park are some interesting towns like Terlingua and the old silver mining town of Safter.