I have my 6' male BCI in a 4'x2'x1'tall boaphile and it works very well. He has enough room to stretch out, which he does often. If I were to change anything it would be to give him a little more height since I know he does like to climb a little.

I would really recommend a bigger enclosure for one of these guys. They are big snakes and fairly active. They will use the space you give them!