Sedan or wagon?
Some posts of interest
viewtopic.php?f=22&t=19256http://azygousadvice.blogspot.com.au/20 ... tback.htmlviewtopic.php?f=22&t=14969http://specialistscaraudio.com/102486.htmlviewtopic.php?f=22&t=13828I thought I'd seen more but I couldn't be bothered looking any longer.
If you go to a good car audio store they can build you one that fits your car perfectly for probably less than you would buy something like that JL box.
In my last car I had custom fibreglass sub in a pretty tight space in the boot and custom door pods for $1000 total (not including the price of the speakers).
I can't remember what the price breakdown was but I would guess a few hundred of that would be for the sub box.
Custom built made by someone good at their job should always give a better result than an off the shelf product.