Here just trying out the cheapest diesel heater currently on Amazon, using it to heat up the oil pan on a 3rd gen 4Runner in subzero temperatures. We try it with and without a tarp and compare the results.

Silvel diesel heater: https://amzn.to/3vS02Tj

AC 120v to DC 12v converter: https://amzn.to/3SjutcD