I decided to start a mouse breeding project and currently have 5 females to 1 male, I had 4 females, but my sister fell in love with one of the mice I bought as a feeder so I put her in there too.

Anyhow, it's coming up on summer here in so cal, and it can get up to 120F outside. I have the mice in the garage, it usually doesn't get above 100F in there, but I know that over 80 they stop breeding and over 90 is a death sentence.
How would I go about keeping the mice cool? I thought about putting a slab of marble in there like you do for bunnies since it never gets hot, but I'm not sure how effective that would be for mice that are constantly running and climbing.


Also, if a female gets pregnant, can I leave her in there, or should I take her out? I read that they are more successful when housed with friends(including the male), but I also read that I should separate them from the male after 16 days together.