I finally got down to the boat to take this Whit. This one angle shows it all though. On my boat, a simple sheet of SS with the two bends you see. The flange is fastened with wood screws on the cabin top and forward wood piece. It extends aft just short of the slide end when it's fully pushed under the sea hood.
The dodger dam (in the shadows in back) was added later I suspect. I don't know when the sea hood was installed or if there was a stock design. I've never removed it and it doesn't leak at all. This would be simple to measure and have bent up I would think. Then cut the forward piece and screw it down.