Golf Guy wrote:
shut everything down except for the furnace that I set at 60 degrees for the night.
Bingo
If you leave the furnace on, it can run your batteries down, easily, overnight. I did that in Yellowstone in Sept 2011. I quickly learned to set the furnace to 45 degrees overnight (it is only to prevent freezing water lines). And that was after running the generator for 12 hours with a Progressive Dynamics PD4655V converter (spelled GOOD CONVERTER) to get the batteries fully charged.
Sleep with a heavy quilt, then jump up in the AM and turn the furnace up.