My wife and I live in Austin but we do not have personal knowledge of commercial RV parks in Texas. We generally stay in Texas state parks which usually have only water and electric hookups and dump stations. If you decide to stay overnight in the Austin area on the way to the Valley you would almost certainly be pleased with the facilities at McKinney Falls State Park on the southeast edge of Austin IF you can tolerate having to use a dump station.
The following link has reviews of both commercial and state park RV facilities in Texas:
Of course you may want to check Woodall's Campground Directory or one of the other directories for additional reviews.
Hope this helps at least a little.