Here's the park's web site and a link to the RV park inside Big Bend Nat'l Park. It's a nice place to stay if you need hookups. The RVs are parked on asphalt with trees and grass behind the RV. If you don't need hookups, Rio Grande Village campground - right next door - has bigger sites and more trees. Either would be your best bet for visiting.
Big Bend N.P. campingAs mentioned, be sure to bring the bulk of food with you. Next to the RV park is a small store but don't count on it having what you need. In the same building is also a nice laundry and showers. There used to be fuel there, also.
Have a great time. It's a favorite of ours.