I came across this site a few year's ago when I was into home audio, and was wondering if anyone has tried this alignment in a car audio situation?

http://www.customanalogue.com/sub_index.htm

Would it work?

People have tried it. But I wouldn't bother. As soon as you stick it in your car, the end result (as evidenced by the frequency response) will not have a Q of 0.5 (or whatever you calculated). The Q of 0.5 is only valid for that theoretical frequency response. As soon as you apply EQ, or room/car gain, or whatever, the picture changes.

In reality the only thing you have to worry about is having a smooth frequency response inside the car where your ears are. It doesn't really matter if the theoretical Q of the subwoofer is 0.49 or 0.9 or whatever.
The difference in overhang/groupdelay/control/whatever is not audible per se and not worth worrying about.

havent been impressed with the peerless subs.

Thanks for that, I really hadn't thought about it like that.

Are you saying that you won't hear the difference between the same sub having different overall Q's (in term's of group delay/overhang/control etc) or 2 different subs that have same overall Q?

The major audible difference between the different Qs is the difference in frequency response.
The few ms of difference in group delay isn't going to be audible, especially in a car (the transfer function of the vehicle will add to that too..).