nice idea, shame about the no enclosure, maybe dynomatting behind it may help a little?
also doesnt help that your sharing the boot air with the 6x9s, got air flow in all directions which surely with the sub having no support of a box wont offer any favours there either?
i like the idea though of stealth boxes and subs built into side panels to give maximum boot space possible, im not one for using up the whole boot space with subs, amps, etc, so i do like this idea