Do you plan to do any wheeling? You have a few options. You could take i10 into Texas and head south to Big Bend National Park. This is one of the most desolate and beautiful places in Texas, so you'll need to be self sufficient if you are camping. It's pretty hot out in the desert at this time, so be forewarned.
If you had straight east towards Houston, you could make a pit stop by Austin and check out Hidden Falls Adventure Park which is an offroad park which also offers full service or primitive camping spots. Stop by in Austin and check out the town, it's pretty cool.
You could also tour the Hill Country and see some beautiful sights and camp at some pretty cool camping spots. We did a 5-day camping trip which consisted of driving, checking out the small towns, and camping at a different place every night.
If you head into Dallas, there are a few nice off-road parks there.
Come into Houston and check out Matagorda beach which offers 26 miles of beach roads which will require 4-wheel drive.
Many options for you