I was reading Martin Simon's book on model aircraft aerodynamics. Here's an excerpt on flutter:

"To prevent flutter it is essential for the hinged surfaces, especially on fast models, to be without slop, and for the wings and fuselage to be stiff. Stiffness is not the same thing as stength. A fibre glass rod or arrow shaft is very strong, but is not very stiff, indeed the flexibility of glass combined with strength is its main recommendation to archers who use it for bows as well as arrows. Some sailplane models like their full-sized counterparts, with slender fiber glass fuselages, are inviting tail flutter at high speeds. Second, the control rods and cables, and all their linkages should be free from free play and gain, as stiff as possible. This does not mean that pivots should be hard to move (although this too will help to prevent flutter), but the control rods should not be easily bent of flexed by end loads. Finally, the control surfaces themselves should be as lightly built and as stiff as possible, and where possible mass balanced"

An excerpt on control hinge sealing:

"With modern plastic materials it is quite feasible for a model to have a flexible surface on one side, so that the joint is fully sealed and smoothly curved, rather than sharply kinked (aerodynamically superior). Some contest sailplanes have adopted this method of hinging for both flaps and control surfaces with very good results"

Hope this helps..............Mike