This is probably something you’re already aware of, but just in case – have you considered putting saucers in the freezer for a couple of hours or so then putting those in the rat cage for them to lie on?

they bottom part of their cage is metal so I wedge some icepacks beneath wherever they lay when it gets really unbearably hot so the metal cools from below… they’re goobers and wouldn’t lie in the saucers if I put them in there unfortunately