I did that before with rubbermaids. Was more difficult to clean the "2nd story" floor though. Just a bit more work. I used pvc fittings to hold the lids/bottoms together. Snakes seemed to like it and it worked well for grayband breeders etc.
If you want a 2nd floor, it may be easier to get the deeper boxes (twice as deep/high) and place a home-made divider that has a hole in it inside. Just one lid to deal with.
Either way, it is good to see others experiment with giving their animals more in the way of choices and stimula.
Keep us posted.
:Mark
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Surrender Dorothy!
www.crimsonking.funtigo.com