Heating units in Aliner or Chalet A frames...

Aframe campers have a relatively low volume to floor space, so they heat very well. Given the limited floor space, I would skip a any floor standing type of heater in favor of a compact table top model. A smallish forced air ceramic heater should do the job. In really cold weather, the furnace can be set to do the initial warm up and then reset to supplement should the heater not be able to keep up. Remember all heaters are equally efficient at converting electricity to heat.

The furnace will wake you up in the middle of the night so cycling at night is best avoided.