Camo, I have been looking at various sources since I saw Dave's suggestion about tapping into the heater. In larger RVs, you are right that there is a big box where the hoses are connected -- that box is the plenum, I think. Unfortunately, my RV is so small that there are no hoses -- the heater is a little box mounted under the stove. The air comes from outside, blows through the heating element, and goes directly into our interior space. This is called a blow-through heater, not surprisingly, and it is the most primitive kind of RV heater.
I need to somehow gain access to the heater and see if there is a way to create a plenum to which I can attach a hose, all without creating a fire hazard! Your suggestion about metal hose is a good one -- mice can chew through almost anything, as I have discovered to my sorrow.
