I haven't done Kajak Sport hatches, but I have done a VCP hatch installation from underneath the deck. Roughen both surfaces and glue it with thickened epoxy. Clamp it securely, but don't squeeze all the glue out of the joint. After it cures, fillet the edge of the ring with thickened epoxy, then lay strips of fiberglass across the rim, fillet and underside of the deck. I used 2 layers of 2"x2" squares with the seams overlapped. It's very solid and it stiffened the deck considerably, too.