For a plywood fin, either finbox compatible or glass-on use 2 layers of 6 oz fiberglass on each side of the plywood fin. Laminate them on an angle so the fiberglass strands run from the base (toward the leading edge) to the tip of the fin. You'll get a better flex pattern than having the fiberglass strands run parallel and perpendicular to the base. Use Resin Research Quik Kick.  To make futures fins I have simple propped up a piece of wood to the desired cant angle (a bit of trigonometry is required) and layed wax paper over it. Wet up 2 layers of glass on the mold, Lay in your wood fin, fill the base with fin roving the width of the wood as well as a piece of roving along the leading edge of the fin, then laminate 2 layers of cloth over that. Over-build everything to trim to shape when cured. Use a carbide jigsaw bit to cut out the fin and base, sand to size and file in the notches for the futures fin. Hotcoat and finish sand to fit into the fin box. You'll want the final base width to be 1/4".