How does sand work on a wooden plywood floor and how deep does the sand need to be?
I would put some cheap nenolium down then a couple inches sand, if you don't put the nenolium down go a bit deeper with the sand so there poop doesn't get the wood wet. Over time I would think some of it would moisten the wood. Here's a good link about sand.
http://www.the-chicken-chick.com/search?q=Sand