The suggestions you have received so far do not match up with your stated plans - in from the north and out through the west. If that is the plan you wish to stick to, you may need to consider Rio Grand Village in the park. It has a no hookup campground, which has some sites with generators allowed during certain parts of the day, and a full hookup site which is a converted parking lot. If you decide to stay at the parks outside on the west, I would suggest driving through the park, setting up and then going back in with your vehicle. Another option is Stillwell RV Park on the northeast side before you enter the park on your planned route. I highly recommend an internet search of the options that are suggested to you to assure they meet your expectations. The distances involved in that part of Texas are not trivial.