Better to use something thinner and more flexible like MonoKote. If you deflect the aileron full up and slide a folded piece of tape (in a "V" shape) into the slot then smooth it down you should get a good seal. If you opt for rudder and elevators, too (I never have bothered) just remember to deflect the surface AWAY from the side you are taping as far as it goes and to pre-crease the tape.