I have outside bins 3'x3' and 2'tall

It is in the shade but I'm in Sacramento CA where summer temps can get into the 100's. I have not gone through a summer yet with my worms and was hoping for some hints on how to keep it cool. It will be shaded and some insulation by leaves. Has anyone use large water bottles to act like a "heat sink". Or should I not harvest and keep the volume large during the heat?

Thanks

Tom