It might be possible to resurrect the shutters method using a different material like aluminum instead of the Coroplast. The Coroplast shutters flexed too much when they were in the open position. I first worked with the shutters about 4 years ago and I believe my experience in building things has grown since then.
I'm thinking about adapting a spring loaded method that keeps the shutters open when the truck slows down enough and doesn't prevent the shutters from closing at speed. The pivot of the shutters behind the grill will be key to how well it responds to the air flow.
