This is how I went about making my first fin. It started by purchasing a 1mm thick A3 size sheet of Carbon fibre. Cut two strips 50mm wide and cover the good face with low tack masking tape. Then chamfered the internal surfaces of the trailing edges (TE). Once done I taped the two TE's edge to edge and applied a thin bead of Gorrila epoxy.
Then folded one side over but spaced them apart at the leading edge (LE) and clamped the TE together. Once cured I cut a 4mm wide strip of carbon sheet and glued it just inside the LE which had previously been chamfered at roughly 45 degrees. Then I used epoxy to glue a 2mm dia carbon rod into the rebate to form a rounded LE
It was then my intension to then push a 2mm dia rod inside the two skins to form an aerodynamic shape. However, as much as I tried I couldn't get the rod more than 12-13cm down inside the fin. So taking a big step backwards I split open the LE, positioned the spacer rod inside the fin and re glued together the LE.
All cleaned up and she looks pretty smart. A careful coat of clear nail varnish (Lacquer) on the LE a file to the TE and another polish and she'l be good to go. 395mm long 49mm wide 4mm thick she weighs 68g