Glad you are enjoying the rats. We breed both regular and african soft furred rats and although their main function is to provide food for the snakes, the rats in and of themselves are very interesting to have around. Well before we ever had snakes we kept rats as pets and personally I think they make the best of the rodent family when it comes to a companion animal.
Try giving your preggo female rats some telephone book pages that you've ripped up into thin strips. They love the stuff for making nests with and it's a great way to recycle your old phone books. Actually all rats love this and I usually toss in a handful or two when I change my rodent enclosures.