I dry camped in a 200 sq ft camper in a brutal winter. Temps were single digits to low 20's with high winds and lots of snow. I bought a programmable thermostat from Wally World for $20. I set it to 42F (the lowest setting) during the day while I was gone beginning at 830AM. An hour before I got back, it was set for 72F. It would then drop to 55F at 11PM and back up to 72F at 6AM about 30 minutes before my alarm went off.
My battery is a $69 Wally World special (100ah) trolling motor battery. The battery would last me three days before it needed to be charged. That included powering the lights (incandescent, not LED) and charging my cell phone on an inverter.
Propane, on the other hand, was a different story. 10 pounds a day even with this low usage schedule. Propane furnaces are not very efficient. I recommend that you use a catalytic propane heater to augment your furnace. You can even refill the 1 pound bottles yourself.
You can go on YouTube to see people who dry camp in winter in North Dakota and how they survive. Also, same source you can see how people refill the little 1lb propane bottles.