There are lots of outfitters on River Road. Wherever you tube, please be careful. There are parts of the river that can kill you. Slumber Falls and Clutter Falls to name two. Get a good map of the river and ask questions.
Here is one trip we took that was fun and easy. Our base was Guadalupe River State Park.
http://www.usaer.com/RV-journeys-2005.htm