the reason i did the litter pans is cause the design i used was built around those. it was off of this site. but is did find one built aroud the mortor tubs and i'm going to build my next one with those. this one suits my needs cause im only gonna have 2.4 breeders. so i figured i can use two tubs for breeding 1.2, the 2 tubs for birthing, then 2 tubs for growing rats. well see if thats gonna work for now but i will eventually build the mortar tub rack when it suits my needs.