I've checked them in our garage on 95+ days here, and the warmest temps inside the coolers were in the low 70's. But it tends to cool off considerably at night here; it's very rare not to drop to the low 60's, even during the peak of summer heat.
I once lived in a climate like that. There are times here during a hot Summer where it is at or near 100 at midnight. That may make a difference. I need to do some testing next August.
