Are you placing the inspection hole(deck port) for a ditty bag to place items to keep dry or actual inspection?  If you want to keep the plain look of the wood I'd recommend ditching a port and just go with a breather valve that's made with brass screw(to go with your brass tow hook) and bungie rigging. Unless you plan on sticking a pipe camera to see the insides coz with a 6" deck port vision is limited inside. 

   I was goign to put it in for a dry bag, but at this point I will probably skip it.  Our first kid is due in march so long trips are probably out of the question for quite a while. :)  

And I'd want to paint the deck port brass or something to match which is probably a pain to do in a way that doesn't flake off.  So just have the bungies left and I'm done.  Just in time for the rain!

I used the 'stock' pads as a template to cut out cork pads.  Sanded the edges.  Used 3m 90 spray adhesive to stick them to the board, and put a bead of silicon around the edges to try to keep them from crumbling.  See how it holds up, but looks pretty good.  Wish someone just made them with a strong edge and a peel and stick back though. :)