If you need electrical hookups Rio Grande Village is the best. Check in at the store. At least the sites are paved so you're not tracking dirt into your camper. At RGV you're in the green belt of the Rio Grande river. Anywhere outside the park you're desert camping. I assume you'll be traveling the park in your Class C. For no hookups you can stay at Cottonwood Campground (no generators, though) near Santa Elena Canyon or at the Chisos Basin Campground. By alternating sites you can cut down on your driving considerably and maybe do hookups just every other day.