What you describe is what I had in mind, but I'm going to use my lower air cleaner plate, held in place by large O-rings, with foam around the underside of the decklid to form a seal.
This will keep crap from being sucked up from under the car and up above the decklid.
Then I plan to fabricate some side window air scoops (or buy some pre-made ones), add some screens to those too, and along with your rubber screen trick, I should have the look I'm going for, with little to no restriction, and it should stay relatively crap-free while driving down the old dusty trail.
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