Yeah, this happened to me as well. When we went to Ft. Worth to pick up our order of 200 mice, I brought 2 long Sterilite tubs with holes all along the sides. The time before that, I took 2 of my mouse tubs, with mesh tops, since I was only getting 100.
We had the AC blowing the whole way home, but by the time we got there, all the mice were soaking wet. I lost 5 of them to the heat. Next time I will take mesh top enclosures again, it's a hard lesson learned