Hi again! Here was my friend's reply about tubing....I did edit phone numbers, but I can DM them to you if you need them. Hope this helps!
I’m not sure of anyone who does “tubing” but there are plenty of people who do rafting. It sounds like they are wanting a more laid back water trip. In that case I’d recommend two programs:
1. Hiwassee River rafting through Hiwassee Outfitters (http://www.hiwasseeoutfitters.com/ (broken link)). They will rent out rafts to groups to go down the Hiwasee. They also have camping spots available. And I bet that they offer tubing as well.
2. Sequatchie River Canoeing:
http://www.sequatchie.com/canoe.htm
This program is less exhilarating but very popular as well
Of course they could also try to call YMCA Camp Ocoee, the Christian camp where I worked for several years. They may be able to also facilitate a program for them.
Another resource for them to look at is Outdoor Chattanooga:
Outdoor Chattanooga
They list all type of great outdoor adventure opportunities in the area