I always seal the hinge gap on the control surfaces. It will help stop flutter, better precise control over the plane in pattern maneuvers. I use clear Monokote or Ultrakote. Cut a long strip of Monokote just wide enough to go down between the control surface and trailing edge and Defect the control surface to the max. Cut the long strip into three pieces, it's easier to seal down than one long piece. Take one of the strips and fold it together the long way as to make a "V" so it will fit down into the control surface gap. Then it's just a matter of sealing it down. I like to have it come out of the gap and onto the trailing edge and the control surface about 1/4".