I wouldn't go smaller than the medium hide as they grow to quickly.. at least a medium you can get a year out of.
Id also re-consider splitting a enclosure if its for a Ball. They aren't as big as you think once you do that. Inside Hight is 10", inside width will be 22 "wide each x 22" deep.. Thats almost as small as a 10 gal aquarium.
Buy 1 enclosure at a time along with 1 snake and get another enclosure and snake in a few months when money is available. You'll be a lot happier with your setup, decision and investment. They look great stacked. Save the $20.
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