Sealing your hinges is a minor aid in reducing flutter. There are more important things that you should pay attention to first...

e.g.

The Funtana is really a SLOW FLYING 3D acrobatic airplane. It should be flown with a wider but lower pitch prop to maximize thrust wjile reducing speed.

Flutter is introduced because of harmonic vibrations caused and exacerbated when the plane is flying over its design speeds.

If you intend to fly it faster than intended, then look to strengthening the linkages and the holding power of your servos and connectors.
The more grip they have, that prevents movement, the less prone the surfaces will be to flutter. This may be more important than sealing a hinge gap.

One of the positive effects of sealing the hinge gaps is the effective dampening of any induced vibrations... so it does not hurt to do it, though often the air passing through the hinge gap is overstated as being a big cause of flutter.


Your primary recourse however should be to keep the plane within it's design envelope.

On my Funtana s90 I have a 16x4W APC prop which gives the plane plenty of torque and pull, but it becomes impossible to overspeed the plane... This was the recommended combo for this plane with very good reason.