I will be using the 5g and small tubs for mouse production most likely. I put a 1.1 in that amount of space and they are fine.

As for rats, I will try and find tubs but more than likely I will have to go with getting them online because try as I might, getting tubs that have flat bottoms (to reduce chewing) are impossible to find. I have found cement mixing tubs that measure 26"X20"X6" I believe. (I'll have to check the measurements again), but I plan on making a rack out of those. I'll try and get some stuff together and take some pictures once I've got it under construction but how many rats could go in a mixing tub that size? I plan on making 2 racks that are 3 tubs tall and that gives me 6 tubs to work with.