I would use a "standard" (approx. 1/8" wide) rubberband. Lay the antenna wire across the rubberband. Put one loop of the band into the other half loop to make a "hitch" around the wire. (Did I explain that OK??). Slip the remaining big loop of the band over the vert fin, between fin and rudder. Adjust the location of the hitch so it's not too tight/loose.