Depending on your mattress and the sturdyness of the milk crates, you might not even need the plywood. It'd be more ventilated without it. And moisture/condensation problems undr a mattress are something to avoid. I have a friend who had to throw away her mattress and platform because of black mold. They have these under bed ventilation pads for boats, but they are kind of expensive. And if you can design something that works for you without one. Why not. Better yet, you have storage boxes underneath it. 3 birds, 1 stone.
~angie
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