The Navik is great. There's no reason to heave the thing into the ocean, though, if you have to take it off. Just remove the paddle (mind your fingers!!!) and then take the rest of the thing off the back of the boat. Stash it in the forepeak.
Buying a pre-made rudder that fits your boat reasonably well is WAY ahead of the game, compared to building one. That is, unless you're after the absolute lightest of light e-rudders and can vacuum bag a foam core with epoxy and carbon cloth. The only downside to a full rudder is the issue of getting the blasted thing lined up - gudgeons and pintles- with the blade in the water. If you just understand that you'll be wrestling the damn thing around for an hour before you get it to work, and that you'll be tired, sweaty and furious by the time it's done, then there ya go. You're set.
Since you opted for the Navik, not a Monitor or Hydrovane, you're going to have to have some sort of non-windvane-attached rudder.
1968 Selmer Series 9 B-flat and A clarinets
1962 Buesher "Aristocrat" tenor saxophone
Piper One Design 24, Hull #35; "Alpha"