I actually have several hatchling size BPs in a 70 series size tub with no hides or decorations, it's a giant tub for such a little snake. I have Reptichip on the bottom and I put the snake all the way in the back of the tub. The tubs are grey and I dig out a little hole in the Reptichip in the back for the snake, they are perfectly happy back there in the dark dug into the Reptichip substrate. I think as long as the tub or container is dark so light can't get through he would be OK no matter what size it is, assuming it's in a tub like configuration. As soon as you get semi-transparent or clear like glass you basically don't have an enclosure at all. Then you need a hide, and basically the hide is your enclosure.