Picked up a couple small ceramic heaters at Wally World (probly <25.00 each). Plug one in reg outlet and the other into the micro's outlet so both can be ran at same time. Though we don't camp in below freezing temps, on the occasions it has gotten downright chilly, we run these 2 units and they do a very good job in keeping rig in sig comfy at around 65* or so. We also keep the pocket door from living area to upstairs closed or almost closed and door to BH open so heat stays mainly in main living area. As a back up, we flip t-stat over to heat just in case it gets so cold the lil heaters can't keep up, so main furnace kicks on 1 or 2 times.