Glen, I've done a bit of experimenting with Hobie's large rudder. Here's a sample:
They seem to come with varying amounts of warp right from the factory, which I guess must be a result of the molding process. This is typically most noticeable on the trailing edge. This doesn't seem to be of any concern to Hobie and it doesn't appear to be an operational problem.
Nevertheless, if you want to put less pressure on your stowed rudder, simply put half of your bungee over the top and the other half underneath, reducing the pressure by half. You can remove additional pressure by pulling slack onto the top half as you stow.