Over a 5 day period we've used a little more than 10 gallons of diesel, a little of that because we had 110v shore power and it wasn't enough to run the coach plus the microwave or hair dryer, so we ran the genset for about an hour and half all weekend. It is a rough estimate because we filled before going out, filled before parking, and filled when we got home. The difference was about 15 gallons comparing the two legs of the trip, the return leg included the fuel used to heat the coach.
It was cold, and we do like to be warm. We had some friends staying near us who had a propane furnace in their coach, and they were shocked at how comfortable our coach was. They assumed better insulation, but it was the AH's ability to push heat.
To me that is a lot of diesel used to heat a small volume, but the alternative is to be uncomfortable. Even with double glazed windows these things leak a lot of heat, and the windshield is a huge loss area even with the curtains closed. The bigger the coach, and especially the more slides, the more you will burn. We have a 42 footer with 4 slides. Nice thing too is that when you leave and head home the motor heats the AH boiler, which keeps the coach much warmer than just the dash vents could, and it keeps the tanks and pipes from freezing until you can flush and re-winterize if you have to.
2006 Patriot Thunder