Putting a 1" or so taper on the leading and trailing edges and leaving them slightly rounded would probably be close enough for the type of sailing you'll be doing. Or perhaps radius the leading edge and put a longer taper in the trailing edge.. either measure will probably get rid of any "flutter" you'd otherwise feel.
Ped's idea of shims/bushings is good, but be aware some nylons and plastics will swell when kept wet. I don't think anodes would be required, just store the rudder dry between trips.
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
Last edited by Faster; 11-27-2009 at 10:40 AM.