Well, I have a giant basketball sized hole in my hood (bigger actually) that Ford put there themselves, and I have an open scoop, and even though my car isn't a DD I've been caught in the rain several times and have yet to have issues with rain getting on my engine. There's a 1/4 inch lip that runs around the hole that seems to be enough to keep rain water out. There are plenty of tricks to prevent rain from getting in. My scoop is more functional as adding hood clearance than letting air in though (I believe this was Ford's intention all along).