Clamp the side panels to each other and then to a work surface long enough to support them. Leave the sheer edge hanging over the edge of the work surface. Apply thickened epoxy to the mating surfaces. You may need one or two helpers to support the loose ends of the sheer clamps as you start clamping at one end of the boat. Do both sides at the same time. Work you way down to the other end of the boat. This may require a lot of clamps, but probably not more than doing one side at a time.