Sounds like you're doing well with the cold. I've never actually camped in the extreme cold (below freezing) for more than a day or so, but we use the RV as a guest house so sometimes the kids will stay out there when it's very cold. The 2 propane furnaces do quite well, but the ducts are not in the floor. The Pergo gets crrrraazzzy cold - that was the only advantage the carpet had over the laminate floor.
The furnaces really suck down the propane so I run the electric heater anyway, even though the furnaces keep up just fine. I don't have any scientific measurements but it has to help reduce propane consumption at least a little.
