that is quite the contraption! man i really hope my family never has to drive behind you though, perhaps a LOT more securing is in order. when , not if, that thing flies off pray that it doesn't hurt anyone!
the idea is sound though. need different materials, maybe hood scoop off old hot rod would work safer and better, or something that shape. then you could put cover on it and be able to open and close it from the inside. maybe even be able to swivel it to not be a water grabber when raining.