I'm not likely to be camping @ 15 degrees, but my wife might use this trailer up north, so the possibility exists....The 4x8 TTT is not insulated, yet (I've got some radiant barrier insulation that I plan to put on the ceiling only, as protection
from heat), and is so well sealed that a cold air incursion is unlikely. Nevertheless, in addition to the 20 degree sleeping bag, carpet on the floor, foam mattress, comforter, quilts,, etc...I have a 200watt Lasko MyHeat ceramic heater

- Lasko MyHeat personal 200 watt ceramic heater
- 41Zz9UNAJ+L__SY355_.jpg (15.58 KiB) Viewed 303 times
. I've seen them used in offices since they came out, and they work pretty good! The reason why I chose a heater drawing so little wattage is all the above reasons, plus the low draw required to run it. If there is no outside 110vac power source, or she chooses not to run the generator, then the 400watt inverter can easily power this heater, and last all night without totally draining the Optima AGM battery. At 80-85% efficiency, the inverter can supply the power needed + power for lighting. If I could have assurance of more available wattage, then I think I'd go with the oil-filled heater, too (it will retain the heat, after the power is gone). Not a bad choice.