Hey Andrew
Wood or fibre?
For my ash, cut off 2 “wings” in foam. Insert tubes etc for the joiners. Sheeting, then for the winglet itself, 3mm plywood core, + 4mm balsa sanded in a profile, clarkY ish.
Vinyl covered et voilà
Alternatively, top rippin, and maybe others, are selling pairs that you can then adapt to your wing.