So I'm wondering... what (if any) species of King/Milk snakes might be suitable to live in an 18x18x18 Exo-terra and not outgrow it?

I've read that grey-bands and mex-mex only get to about 3 feet long so those might be candidates, not sure what other species might be a good fit or what species might be more arboreal than others and make use of the branch to get more living volume.

If you don't think 18x18x18 is big enough for any sort of king/milk are there other species you might recommend?

Thanks!