I took an old candle and carved it to shape with a plane. You can see in the photo above the candle and next to it is a mast tube for Al's boat. The candle is wrapped in fiberglass and epoxy. When it is hard it will then be fitted in the hull and cut to fit. This step will probably be done when the keel box is fitted to the hull.
The top photo shows the candle wrapped with fiberglass and epoxy and setting up to dry.