Good points all. FYI, I keep the cowls inside the cabin storage area--only plan to put them on when I am in the cabin and need ventilation. Reasons: 1. keep animals (squirrels, etc.) out of the dorades when boat is sitting in the yard, 2. when climbing to the anchor well cowls can be kicked off and fall in the water never to be recovered. Now you have made me aware of a third reason.
I am using the flat plates that came with the cowl vents to replace the cowls. They don't screw in, but still they are hard to remove and I'm sure will stay in place.
You have made me think about putting deckplates in the bulkhead and opening them only when I need ventilation. Looks are not as important as function. I don't plan to be in boat in dire conditions, but they can't always be avoided. I have a friend who lives in Wisconsin near Lake Michigan and we may take his boat and my boat out on that lake--so in that eventuality I definitely need to be prepared. (They ought to call the Great Lakes inland seas, not lakes.)