If you have the patience, an 8" SONOTUBE, 6.5" Kicker 08CVT654, fiberglass and resin you could build something like this. I'm not finished yet still needs more glass, fabric and armrest. Much smaller and still leaves room behind the seats. Sounds awesome.
I don't know how to post pictures yet so Image shack is doing it for me.
I had a diamond 10" sub hooked up to 300W amp that beat hard as hell for a 10"....It went from a camry to a fireturd to an altima before the amp blew...now it is in a 2009 or 2010 honda accord and still beatin harder than a lot of single 12"s...maybe it's the ported box, but doesnt change the fact that it is a durable lil guy.
Keith has the best looking, best fitting custom box in his Ranger that I've ever seen....hands down. No tube BS. That box ain't goin' anywhere...and if it does, it's goin' in my truck!
Keith...when I was in the market, I looked at almost all those you are looking at...but all mine were non-shallow specific subs. I've had a Kicker Comp VR for the past 5 years and man, it's a GREAT sub. She's a CVR12-4 powered by a 400.1 kicker mono amp. Kicker bro, kicker.