by Redneck Packrat » Sun Jun 11, 2017 7:56 am
Dead air is as effective, arguably more-so, than insulation. Nothing to conduct heat, convection requires movement. I'm not so sure that your GS between things isn't hindering very slightly. Try a strip of tape around the outside where the lid sets down on the box, maybe? It's all about stopping convection with materials that don't promote conduction, and minimizing radiation, and at the same time *inducing* convection inside the box from the foods to your heat sink (ice). Shape of the ice, location of the ice, arrangement of the heat donors (canteen, steaks, etc.) and the surface area of the ice.
Ice boxes (not refrigerators, their predecessors) had provisions for the ice being at the top of the insulated box, with a pan and drip drain to keep the food (semi-) dry.
Not saying any of this will actually work in a mobile cooler situation, but just throwing out the list-of-wants that you might be able to incorporate somehow.