My 2008 OFF-ROAD RT14 POPUP has the big propane furnace in it. It puts out too much heat for my small floorplan and very seldom gets used. It is also very loud and will most definitely run us out of the trailer...
I started to do one of those water heater hydronic heat radiators but never got it finished... Ordered most of the parts to build it up but never went anywhere with it. I think this would be perfect for us for heat. Since it is a closed hot water loop I don't think it would be hard to keep the hot water up with the propane fuel.
Would look something like this

I use the MR Buddy heater most of the time when we are awake... When we go to sleep we have enough covers to not need any propane heat...
I did do alot of closing up air gap holes around the trailer and tent beds ...
Roy Ken