Next you take plastic material and cover the form. Stan uses polypropolene. It is stiff and releases from the resin. Test any plastic you plan on using with your resin to make sure the resin doesn't destroy the plastic and also that it releases when dry. Obviously, you should do that NOW if you haven't done so alreadly ;-)  The plastic is .02" thick and a double layer.  It has to hold the wet fiberglass and filler.