It will stick to plywood fine but it won't be smooth. Which I don't think really matters in a snake room. If you want it smooth then you put down a thin board known as luian (sp)

The sealing job looks great, do you have any source for the bldg to breath?
It shouldn't be airtight.

Looks like it is gonna be an awesome snake room and I can't wait to see it when it's done