RE: How to make a mould of my cowl?
Well, that's the basics of it. You still need to plug thoes holes and build some sort of flange or trimming edge. Wax, PVA and then your ready to apply your gelcoat, a nice healthy layer of it. Let that cure about an hour and fill your hard corners with a bog of resin. Layers of fiberglass MAT are applied immediately after that while it's still very wet. 2 layers is a nice application at a time as it won't get too hot as it kicks off.
All these details are found in many areas of these threads we linked you to. Same rules apply to your hatch AND the hull.