well seing how your question was sort of lost in McKinseys explanation.

I found these 74qt sterilite tubs, that are 3.8'x1.8' and they are actually really nice tubs. I keep my boas in there for now. Of course this is when they are adults.

Babies are gonna grow through tubs faster.

Start with what jimi said. Put them in a 6qt, when they outgrow that jump to 12qt when the out grow that jump to 21qt etc etc. You can find different size tubs with the same height (usually). That is how I built my rack. so I can interchange tubs if need be. My 12's are the same height as my 32's which are the same height as my 74's