True, they are not totally sealed, but at the same time they will not act as necessary to keep the front of the sub separated from the rear and will therefore suffer from cancellation and muddy sound.

SUV's are typically not designed for use with an infinite baffle sub - every sub I've ever seen, including those from the factory, come mounted in an enclosure.... Too hard to tune an area such as you are discussing (since you can't easily measure the volume) and too many things to vibrate (wires, etc).

d-