I'm not a huge fan of the way he built the "box" I just don't like that expanding foam stuff. It tends to break loose over time and can cause more of a headache than it is worth.
That said, I've seen those kinds of set ups before and they aren't bad.
Well, I've heard one that was just flat terrible, but it had no tuning at all.
I've heard others that just used 6x9's back there and it sounded rather good. Not sound quality competition good, but tons better than it was.

How much space do you have to work with?
There are some options for shallow mount subs that all have a decent sound.
and some subs, like boston acoustic that don't need as much space, ie, .75 cubic feet versus 1 cubic foot.

I'd also look real hard at infinite baffle set ups as that would make the install a good bit easier... or at least, it could make it easier since you wouldn't have to make a box using the car itself like they did in that build.