Guys, I've got a similar ASW-28 that has the same winglets. Although not the FMS (it is an ST Models and only 2m) I used and old thin cotton bed sheet, Super77 and Zap medium CA to make the winglets wicked strong. Just soak the cloth, sand and paint. Did the whole fuselage too, this sailplane glides well now.
This is how strong they are...
Build thread here