RV elevators and rudders are simple hinged control surfaces where the aerodynamic influences of something like gap seals would be unlikely to ever have any negative effect on flight / handling characteristics.
The same can not be said for the ailerons (including the flapperons on the RV-12).
Aileron performance is actively influenced (by design) by the shape and the way that air flows around them. Making changes that influence that flow will definitely put you in the experimenter category.