Thanks for your time and replies guys. It doesn't seem like they smelled as much when I was keeping them in their "baby tub" setup.. Of course, they were babies then too. What's odd is that the females tend to smell far worse than the males (I guess they're peeing all over their cages more).

I may wait until these rats get older and breed a single litter to start with (trying out a tub setup to see if it helps with the odors). I'm not sure how well my current ones would adapt to a smaller tub setup now that they are used to being in cages.

If only I had a shed to keep them in outside, this wouldn't be an issue.. Alas.

Thanks again for your time and advice!