Wonderful Nick, here we come exactly to the point! My idea was to laminate carbon-fibers between the 2 last layers of plywood to replace the original galvi-sheet that went all around my stern, have the woven carbon-fibers opened up just right for the size of the bolts to go through, and have the head of the bolts sitting inside the last layer of plywood. I would filler around the boltheads to get a flat surface, and the fibreglass with Epoxy goes over it. Like this no water can come in by the bolts, and if there should be a problem with the bolts one day it's easy to sort out.