You can get submersible tank heaters, then pair that with a small underwater turbine (like for salt water tanks), that will keep the water moving around so you don’t get hot pockets in there. You may want to change the vessel if your going to put an active heating element in there, as the foam cooler may not like that so much. If you could intersect the internal temp sensor of the tank heater though and tie it in with your submersible thermometer and use something between those two to actually control the temp, you’d be in serious business then.

Also, it might be easier to just thaw the frozen steaks. Or, put one in the box frozen and check it every half-hour to see how long it takes to thaw, then add on your cooking time.

How about cutting an appropriate sized hole in the cooler and sticking the business end of an infrared (remote-sensing) thermometer that points at the meat but has the temp readout on the outside?

Very interesting post. Makes me want to try it myself. Thanky.

Cool write up all around.