The biggest problem with the Truma is it is a slow heat system. It can not handle large temperature changes or that much even quickly recover from leaving the door open for a few minutes. Therefore, I don't like it because I get a lot of energy conservation by letting the temperature drop when I don't need the camper warm like at night or out hiking for the day. The rest of the time the temp is as low as the thermostat allows. On most days, this means a quick one time rise to 70* in the morning and then a couple hours in the evening. The Truma won't handle the large quick swings in temperature. 20* reduction in temperature saves a lot of propane.
In regards to a wave heater, since they do not exhaust to the outside, all the moisture from the propane burning is inside the unit. I have enough problems with condensation from breathing and limited cooking, so I don't want my heat source to also add moisture. The furnace is a dry heat because the exhaust is vented outside.
Lastly, I would much rather have a $700 furnace and a $300 water heater that can be repaired/replaced independantly than a $2300 combination unit.
