Don - I know you have discussed this before but did you play with the HYDRONIC method heating using the MH water Heater for source of hot water in the heat registers. I remember you saying the power to keep the water heater hot wasn't all that much with its normal cycling.
Running a couple of Hydronic heat zones around the MH might help out alot...
When I get back into the off road trips again that is definitely going to be my primary source of heat for my OFF-ROAD Trailer. Will do away with the OEM propane gas heater and blower system. I will only have a 4000BTU heat system and a good blankets haha... My battery system already accommodates me using a two zone low wattage electric blanket.
Of course my small floorplan is quiet abit smaller then yours but the idea is still there. Hydronic Heat is a very clean heat source.
Roy Ken