Seconding the suggestion to just put it in an empty cooler stashed somewhere in the car where no sun will get on it. Avoids condensation, and as long as it's not in the sunlight it shouldn't heat up anywhere near enough to be a worry.
You can also test it out by throwing a zippo or some change or something in it for a day, see how hot they feel when you go out for a break.
You can also test it out by throwing a zippo or some change or something in it for a day, see how hot they feel when you go out for a break.