It is still a little early for the pop up eclipse RV camping spots to start showing up, for those I would suggest checking back at 18-24 months before the eclipse.
Having said that if you want an off grid dry camping spot or state park like setting, there are a few I have considered. First off the path of this eclipse is a LOT wider than the last one meaning it is much less important to be right at the center line. The path also goes through several major cities including the entire DFW metro plex.
Now down to sites I have under consideration in no particular order:
1, Lady Bird Johnson park RV campground in Fredericksburg, TX. This is a city park with a full hookup RV campground, spacing is somewhat tight between the RV's and the older part of the campground has a lot of oak trees, however I strongly suspect there will be organized observing going on somewhere in this large park.
2, There is a dry camping only commercial RV park / ranch between Fredericksburg and Llano also near center line of the eclipse, Oxford Ranch Campground, we stopped in there on a day drive while in the hill country a couple of years ago, office was closed, signs on the door sounded less than welcoming, though that may be a false impression. (very close to center line)
3, Garner state park, the most popular state park in Texas, and is is withing a fraction of a mile of the center line (good luck getting a site, in normal times it is hard to get reservations there in the busy season)
4, Llano city RV park, in small city part on a small dammed up river / lake, can't comment never been to the park, but have been to Llano a couple of times, (home of Coopers BBQ original location (now a chain) considered by many to be the best BBQ in Texas)
5, The centerline crosses Lake Buchanan where there are a number of RV parks, as well as a couple of public RV campground (COE?)
going north there are any number of other commercial RV parks, and a few public ones along the path.