: The basic idea is that when you create the opening you have about 12 inches
: of excess material on each side. This material is then brought together
: and folded sharply over a chine -- which could be a 1/4 inch cedar strip
: or a plastic strip of similar dimensions. Roll this three times, just as
: you would seal a drybag and it should lie flat along the deck. It can be
: off center if you wish.

: This creates a waterproof seal along your 8 foot length.

Good thinking. I tested a similar rolled up skin closure a few years ago,
but found mine to be a bit awkward to roll up over such a long span, plus
a little bulky. However, it would certainly be waterproof, just like
on the dry bags you mention. I may give it a second look, as at the time,
I wasn't looking for waterproof as much as I wanted it to look good.

This method might even work well without a zipper, by using just a flap
that is glued on one side, and Velcro's on the other as in the pic I attached
to Brians post. The flap would need to be wider, and the Velcro could be the
2" type instead of the 1" shown.

Thanks for taking the time to respond. It's a workable solution, and gives
me another viable option.

Tom