I made a simple pot cozy for the Walmart Grease Pot. It’s just a cylinder of Reflectix insulation and aluminum tape the height of the sides of the pot, with a circular piece for the bottom. A second short cylinder and circular top cover the pot’s lid.

Here is the result of a kitchen test:

Test 1, with cozy:

Temp 61 deg. F
1 pint water to rolling boil, placed in cozy and covered.
45 minutes, T = 158 deg. F

Temp 59 deg. F
1 pint water to rolling boil, covered and let stand on folded kitchen towel.
45 minutes, T = 135 deg. F

After 45 minutes, the pot in the cozy was still at almost a cooking temperature (160 degrees is a good sterilizing temperature) while the non-cozy pot was much cooler. The difference would probably be much larger outdoors, where wind would cool the uncovered pot faster.