Obviously a lot of good opinions on what to use for the bulkhead. Fortunately you have a flat back deck for a Beckson hatch.

When I put a bulkhead in a stripper, I just use thickened epoxy. When the bulkhead is made and shaped best you can, push it in position from the back oval hatch and go around it with a pencil marking the location on the boat. Then sand the pencil area clean of any mold wax etc. Put the bulkhead in (and you will have gaps) and I just use my finger with a glove and push a bead of thickened epoxy on the joint on both sides. It will never come out. You can use a mirror and drop light to see what you're doing. You will be working by "feel" on the Beckson hatch side.