My bulkheads are the same 2x6 material as I used for the stringers, they are three piece and are glued/screwed in place, then glassed in. Used pour foam in the cavities before placing the floor. Just a little foam at a time, when any got up a bit high, I used a bow saw blade to shave a bit off. Just how I did it, maybe not the way others did, but I've jumped the boat twice completely out of the water, and no stress cracks have appeared anywhere(knock on wood). Given the craft is in inside storage all the time, the floor/stringer replacement will likely outlast me.