you may be in luck. I have 2 sub enclosures custom made for my frontier that I'm not using. Just so you know, I have a 1999 ex. cab. The first box I built is made to fit directly behind the passenger seat. It has 1 cubic foot of airspace inside the box and is a sealed enclosure. It's made out of 3/4" mdf and is built to fit around the 7" hump in the floor.
the other enclosure fits very snuggly into the recessed area of where the jumper seat would normally be. I removed mine and built an enclosure to fit into that area. I don't wanna brag, but it came out to be pretty nice. I even angled the baffle for the sub, sealed off a section in the box for the possibility of a 5 1/4" mid to be installed (for rear fill), and extended the bottom portion of the box across the floor so the sub port would fire under the passenger side seat.
unfortunately, I don't have pics of these however I may be able to take some fairly soon. The recessed box had my amps mounted in a an angled amp rack on the back wall, and was intended to be setup with two 12" subs on either side. I only got around to building one box before I changed my mind about my setup. The other enclosure that fits behind the passenger seat does require that the passenger side jumper seat is removed, but this is also an ideal place to put your amp and possibly capacitor, since the battery is on this side of the truck.
If you have any other specific questions about areas, layouts, designs, etc... please feel free to contact me. I've tried several different setups in my truck, and plan to keep trying different things. Currently I'm pushing a single 12" Diamond audio TDX sub with dual 2ohm coils and am using a directed audio 1100d amp. (1400watts @ 1 ohm!!!) My steering wheel shakes at 3/4 volume. it's nice. I think an ideal setup is going to be 2 10" subs behid each seat, but I'm going to try another ported box with this 12" sub.
Anyway, get at me at
gmeade@tmail.com if you need some help.
-Geoff