I'm assuming you mean the overall enclosure rather than the hide.
The short story is that the fewer holes there are for air exchange, the better. Jeff Clark, one of the big rainbow experts in the US, has stated before that while most snakes do best with lots of air exchange, rainbows do best with little. This keep the temperature more stable and the humidity inside where you want it. Screen tops are horrible for these snakes.
What type of enclosure were you thinking of?
Cliff Earle Living Gems Reptiles Premium Brazilian Rainbow Boas from a disease-tested facility Website, Facebook