Depends on what you want? If you truly have gelcoat in the anchor locker then I would gel coat it as well. Marine Tek is an epoxy resin. Gel coat is a polyester resin material and will not stick to dry epoxy resin that well at all. If you planning on Marine Tek and done, then ok, it will seal the hole. If you are planning to cover with gel coat and sand polish to make it seamless, then I don't think it is going to last all that long. IMO.
