here is a easy way with good results. take some blue or pink foam and carve it to the rough shape. then sand it,it sands easily. wrap the finished plug in packing tape so resin wont eat the foam.then glass it with a few layers of cloth. sand to a smooth finish then pour acetone in to eat out the foam. this is way easier then it sounds, i use this method to make complete fuselages. i have taken pics of the complete process, if your interested email me and i will send them to you.

ps. i forgot to mention for a final coat , i mix microballoons with resin. brush this on the plug. it will be easier to sand to a smooth surface.,and your less likely to sand into the cloth.