I think most would use 3/4 marine ply and 1708 mat. Poly or epoxy either would work.
The main thing is on a bulk head is not to fasten it directly to the hull or floor. This will cause hard spots and then you will get stress cracks around where it is attached.
Go to page 2 of my rebuild. Post #62,scroll down and you will see what I (mean) did. There is space between the bottom and sides. The glass tabbed to bottom and side will be strong and will give the necessary strength.
I am sure a few more will chime in...as there are various ways of doing anything.
