RoyB wrote:
Go get a 50-foot or longer extension cord and run out to the truck from the garage and plug in a oil-filled heater...
That would be my plan A...if that's not possible, then plan B:
Leave all the cabinet doors open, turn on the furnace and set the t-stat at 40*. Be sure all roof vents etc are closed. If the sun hits the camper on one side leave the blind or shade up on that window.
During the day the sun will keep the inside of the camper warm, and if inside temps drop below 40 at night the furnace will come as a last resort.
Even with one battery this should get you by for a couple days.
