Not quite sure why you want to have the plywood center. I put wood bulkheads in my boats because I'm working with wood to build the rest of the boat. But once you rim the bulkhead with foam, it seems to me it would be just as easy to put in a solid foam bulkhead. Since I built my last boat a couple of years ago I'm pretty much convinced that foam bulkheads are at least as good as wood, especially with some of the hi-tech adhesives available.