You know, one possible upside is you can actually do experiments now with your defunct devices. Try the same setup, place the broken devices in there, but use some kind of moisture/humidity detector, as well as a thermometer, to see which factor is likely to be most critical factor. My own sense is that if the humidity is high, you could get a steaming effect if you simply closed in very humid or moist air into the box and then the greenhouse effect does the rest…
You could try: clear case, ice packs inside ziploc bags to cool things off, dessicant inside clear case to remove water vapor. That’s a whole setup though.
Of course, all this assumes a lot more time on your hands than I’m guessing you have… You probably just want to hit upon something that reliably works without so much fuss.