We insulate the heck out of our RV (Reflectix over the windows/foam "pillows" in the vents/AC ducts closed, etc) for starters, then use both electric and the furnace for warmth. Our electric heater has a digital temperature setting, so we set that at 67 degrees at night - and the furnace at 65. The furnace will run a few times during the night; but one night during single-digit temps (we were winterized at that point) - our furnace came on a couple of times, and the neighboring 5er - sheesh, I could hear their furnace kick on about every 10 minutes....