We used to fill the electronics in the case with "potty" (resin) up to the top, even milspec and automotive grade. They get warmer but way more gradual, don't m

We used to fill the electronics in the case with "potty" (resin) up to the top, even milspec and automotive grade. They get warmer but way more gradual, don't move, and if you can keep the heat within the normal range the thermal stress gets less by avoiding sudden temperature changes. Though the main failure mode was due to EMI as coil and spark plugs generate all kinds of crap.