I live in the desert where 115 degrees are not uncommon. Trying freezing a gallon milk jug or something similar and putting it in their water. It will last a few hours. I would think maybe try doing a dug out where young into the ground a foot or two, lay some lumber across the top and cover the boards with a foot or two of dirt. Make an entrance away from direct sun and I think this would provide a cooler place for them to go in the hottest part of the day. Its cooler underground. ;0) Or just take a large cloth and stake it a few feet off the ground to provide a shady place for them to go.