I've now managed to chisel off as much "Bondo" as possible and removed all silicon with "silicon eater". I've made a template for the opening. There are a few places where I have to cut and sand to level the edge slightly. I didn't want to make too much dust today, out of respect of my neighbour in the boat yard who had just cleaned and polished his yacht and was also painting on antifouling. So my plan is now to fill the small holes. I will then cut a couple of panels to size and glass them into the existing opening. I'll probably have to put a couple of layers of fiberglass in between and also build up with cloth/resin in the cut out areas on the top where the hinges used to open into. Once that is all done, I'll fill and smooth the rim around it. I will not reuse the old Lewmar hatch, it is really too big for the opening. It was in part only supported by "Bondo" but would also only fit by making a recess for the hinges and building up where the original water run off in front of the original hatch was. I will get a smaller new hatch sometimes later this year, but as the sailing season is starting, I really only want to get it water tight and safe for the moment.