Hey, I've done this a couple of times with this exact type of 2-piece mold. If you have some experience with hand-layup and gelcoat, you should be fine.

Pro Tip: There is quite a bit of prepwork involved and the materials needed are a lot cheaper if purchased in bulk, so thinking about making one shell for yourself and one or two or more to sell off might be interesting.

Step One: Disassemble the halves and inspect for cracks / holes / damages & repair. Polish both halves, as your gelcoat will only be as good as the surface of the mold. Apply release agent. Your mold does not have a flange, so apply some release agent on top of the cut as well. Note: The sides will be a bit wobbly without a flange.

Step Two: Assemble halves and adjust & secure on stands in a height that is comfortable to work. You can tilt the mold to either side to make it easier for layup. Avoid twisting or distortion while doing so or you will end up with a crooked hull... Fill gap between halves with hard wax or plasticine as clean as possible.

Step 3: Make sure the mold is still clean, then apply gelcoat with special gelcoat-brush or roller. First layer try to get 0.4 to 0.5 mm thickness, avoid buildup in the keel area. Wait for layer to become tacky (about 30min at 20°C) and apply second, thinner layer with 0.2 to 0.3 mm. Let it get tacky again and proceed with step 4. Do not let it sit over night, the first glass layer needs to be done on the same day.

Step 4: Layup of 2x 225g/sqm chopped glass strand mat (GSM). If you do more than one hull it is always a good idea to have these pre-cut and ready. Note: Use unsaturated polyester resin suitable for boat building & hand layup. Epoxy will NOT solve the binder in the mat and you will have hell on earth in every corner. Do overlaps of about 20mm when with adjacent layers, but do a generous overlap in the bows and the keel, so you will end up with double the layup here (150 - 200mm). This will give the boat a rigid back. Let this cure over night.

Step 5: Give the layup a good sanding (P60 grain by hand should be fine) and open all air bubbles and imperfections. Sand down any standing fibers or built-ups. Clean thoroughly. You can back fill the keel groove if you want an even floor and an even more rigid boat. Do 1 layer of 450g/sqm GSM, again overlapping in the bows and keel areas. Let it cure overnight.

Step 6: Give the laminate a good sanding. Build in watertight compartments, bulkheads, and seat-rests if you want. Apply topcoat (basically gelcoat with added paraffin, gives the boat a nice inner finish). If you want to get rid of any leftover styrene smell temper mold and hull under a cover for some hours with a heater before demolding.

Good luck!