lows below freezing, bad idea to camp?

One trick I've done in an area that allowed generators until 7-8 PM was to use an electric space heater on its own extension cord threaded through the mousehole at 1500 watts, and another heater at 750 watts. I went about my business with both heaters cranked. Then when it was time to retire, I put away the electric heaters, fired up the propane furnace, which was easily able to maintain a comfortable temperature even with the outside weather being in the teens.