I already have a box which I made to fit a 12" kappa perfect sub. It's not the prettiest thing but it works.
I personally would not want a sub box that is molded to be a part of any of the vx's interior pannel because the panels are expensive to replace. This means the boxes themselves would be expensive if they come with the panels, or it means I would have to cut up or modify what I have and then have to deal with paying $ to return the VX to factory spec if that day ever comes.
I would be more interested a box in either of the following froms:
1) A fiberglassed, countour fitted box that sits in one of the rear corners (Driver side would be best). This box would be in the way somewhat if you load/unload large objects. However, for daily use it'll be OK. Problem is access to one of the tool/jack access panels would be blocked. So it would have to be somewhat removeable.
2) A box that is similar to the rear cargo storeage box Tone showed a while back (I think it was Tone) where the top of the box is level with the seat backs of the rear seats when they're folded down. If you can build in some storeage bins, that would be even better. Also, it would be best if the sub mounting surface is counter sunk so that if you do put cargo on top of everything, the sub won't get in the way and get damanged. This will allow room for sub grills to be installed. And, for those who want a stealthy appearance, what if you make it a down firing system? Anyone looking in won't see any subs at all.
If 12" subs are too deep, then I'd say go with two 10"s. 10s are best for tight, accurate sound reproduction. They cost less, and sound absolutely amazing. I had two entry level JL 10W0s wired in parallel once in a VW hatchback and it was the most versatile bass system I have ever heard. From tight, well defined punchy bass to low frequency rumble, those 10s handled it all. I listened to just about every kind of music there is from classical to hip hop and those subs played them all beautifully. The two subs together didn't even cost over $100.
Oh.. btw, I'd go with sealed enclosures. No porting should be used if definition is desired.
If anyone is interested, there's a company out there who makes really nice looking sub boxes. Not a custom fit, but they do look good. The brand is Element Enclosures. http://www.audio-n-more.com/element_...enclosures.htm