I crown mine slightly.
I see two ways to do this.
Assemble the deck by gluing up beveled pieces, like a old Oak whiskey barrel, or do like I do, start with 5/4" thick stock. Make sure the bottom of the deck is even with the bottom of the gunnel, and the excess is above the shear.
I rough bevel on a belt sander, before fitting, and finish after installing the gunnels.
I'll try and get a better pic posted soon.
Jim