Im building a downfire box for a porsche carrera and it will be a downfire box. the only question I have is how much of a gap will I need. Its going behind the back seat on top of the factory sub location. the factory contour is slightly round, so on the sides I have about 2" and in the middle I have about 1" but with the speaker in it will only be about 3/4" in the middle and 1 3/4" on the sides. will this be enough. Im thinking about scratching the box and doing a fiberglass one, seems a little bit easier right now and will look better imo. any help will be greatly appreciated.