I agree with Tom, you need at least two litters born every week to keep up, they can have a litter every 3 weeks born back to back but you'd want 1.3 since one might not take or litters may be smaller, minumim of 4 groups breeding, one week apart from each other. Most people use morter tubs from Home Depot or litter pans if you are doing a rack setup. That would take up the least amount of space, you can build your own easily.