TexasStar - If you open the rear door on the sofa you will see the heater ducting. The middle door will give you access to the hoses. They exit through the floor right above the LP tank.
Check those hoses! If they are slow leaking into the carpet (why AS carpeted under the sofa around these hoses escapes me, then they could cause rot in the OSB floor (I have a little around the holes themselves). Or, like me then can blow and scare you half to death.
Here is what happened to me:I am an Idiot Post
BTW - these continue further back on many 345s to the water heater as well.
Basically the routing is as follows: the two original heater hoses Y off of the outlet and inlet between the radiator, water inlet and front heater core [original routing]. They run along the pass side floor, across the transmission and down the driver's side of the coach where they Y split again into the aux heater, and then they finally end at the water heater.
Mine were probably never replaced even though my main heater hoses looked like they were. I ended up replacing my main heater hoses and inserting a loop on the first Y to bypass all of this since my aux heater fan was out and needed repair. Besides, its cold I didn't feel like running 20' of hose under the coach. Now I just run the front furnace. Although I do miss the free hot water when I stop.