We stayed at the CG behind the motel on HWY 170. It's basically a dirt parking lot like a lot of desert CG. The other CG were not open when we were there but the couple we looked at had very uneven ground, at least the place we stayed was flat.
I can't comment on the in-park CG as we didn't check them out. Many years ago we stayed at the CG by the river, Rio Grande Village. All I really recall is that vultures were the campground pest. The CG has concrete tables with a concrete 'V' rook and the buzzards would land on that and eye you as you ate. They also had fights. Don't know if that is still the case tho.
If your vehicle is up to it do drive the River road, it's a great trip and it takes you thru an old mining camp ghost town. The road was in good dirt road condition when we drove it but you could see that it was recently graded. Check with the rangers before driving it.
Under no circumstances should you try the Black Gap road unless you are a serious off road driver with a well equipped vehicle. We drove almost all the other roads with no problem, we have 4WD but did not need it.
The state park: Big Bend River Ranch is worth a drive thru. There is a movie set that has been used for a lot of Western flicks, No Country For an Old Man for one. It's out on Hwy 170 past Lajitas. Speaking of Lajitas it reportedly has a RV Resort type CG there. It's about the only green spot around that's for sure.
Stock up on everything since everything in the Terlingua stores is pricey. They have a mini-super market now.
Arctic Fox 25Y Travel Trailer
2018 RAM 2500 6.7L 4WD shortbed
Straightline dual cam hitch
400W Solar with Victron controller
Superbumper