I agree with the common view that the furnace fan does draw considerable power from the batteries and you'll be unlikely able to run it for 8 hrs/night for two nights. We camp in the cooler weather and will set the furnace to about 40 degrees (so it rarely turns on). We have a nice comforter on the bed and I sleep with a stocking cap and socks. We sleep great. When I get up, it is a little cold. I change the thermostat to 60 degrees and the MH warms up in a few minutes. By then sun is streaming in and that helps also. Even so, I need a generator to charge the batteries (I have about 250 amp-hours) during the day.