TexasStars, I have mine removed from the AS right now. Like Al's my valve was all corroded. Try hitting it with a wire brush and then soaking it in CLR (Calcium Lime Rust remover) for a night.
This mane mine functional again. I got a price on a GM heater valve once from PepBoys and I think he said $100 something - I can't remember because I think I stopped listening at about "one hund..."
You should have the same couch as me. You can access the heater from the three doors on the front of the couch, but honestly to really get at everything remove the couch. Four bolts on the back rest hinge and four more for the hinges toward the back of the frame and it's off.
It's possible that it's leaking at the valve itself but its very likely that it's where the hoses pass through the floor. You really can't tell until you can sit there (where the coach used to be) and see everything.
Don't forget that these hoses run down to your water heater from here. There are four Y-connectors and 30 feet of heater hose in all of this so if the hoses are bad on the aux heater then they are bad all the way down.
Good luck on this and let us know what you find out.