Gotta love people input, "Good job at failing...." with not actual design help.
Anyway, I've seen some factory doors that open with as air flow across the radiator then close when stopped, some are just plastic doors on a loose hinge to a riveted piece of light rubber (I'd use sheet Buna, like 50 to 60 Durometer). At a stop the fan will pull them closed and pull across the core.
My concern is clearance to the water pump snout, based on what I see on my set up. But you're designing so that's probably taken into account.
