I was wanting to do this as well and did some research...
This is the concept
This is what I wanted to experiment with...
I would use these two type of heat exchangers
I found one guy that had great success with his smaller TT trailer doing this...
Doesnt really look like a hard thing to play with to see how it work for you... Another guy on here has done the same concept keeping his fresh water tanks and lines heated up from freezing in the winter..
I think it would work like gang busters in my OFF-ROAD POPUP trailer and replace the way too hot and loud for us being the OEM propane furnace. The AQUAHOT 200 heater exchanger with built in axial fans would fit right into the spot where the OEM Propane furnace was installed...
Roy Ken