Just a couple questions/observations. Sorry if I missed the answers but I did look back...

How thick is the slap that will rest on the plywood/steel base?

Is there a chance the adhesive this guy is using would be flexible enough to accommodate the maximum wood dimensional change?

Slots to accommodate wood dimensional change will need to be in both the steel and the layers of plywood on top of it.

Not it sure I am adding anything but I am curious. 😀