There are several Thousand Trails campgrounds in Texas. There is one about 6-7 miles from where I live in Lakehills on Medina Lake and I know there is another in Conroe. The price they charge is worth it if you camp frequently and stay at TT campgrounds pretty much exclusively. We don't camp this way but like to try many different camp grounds. As a Texan who will likely travel in Texas, check this site out:
https://texascampgrounds.com/free-camping-guide/
The free camping guide also includes a member card that gives you a discount at parks that are in the guide. We are also members of Passport America and have saved hundreds of dollars a year using their member benefit. They have a map of participating campgrounds on their site and you can see if joining makes sense to you. The 50 percent savings are typically restricted to a couple nights and campgrounds don't allow a discount on holidays and such. That suits our camping style but perhaps is not for everyone.
Good Sam Club is owned by Camping World has has more parks participating than Passport America but costs a bit more to join. They also offer other things with a membership. Here is a list of parks in Texas that participate; check their other "benefits" to see if these make sense. rv.net is owned by this bunch and you can read comments on the other benefits.
As you can see, there is no one right answer to which camping discount club/group is right for anyone.