I did a complete R&R on the OEM system in my Honda Odyssey a few years ago, and to solve the Sub-Problem, I stumbled onto the best sounding system the installers had ever heard...for under $25.00
I bought a 10" used Bazooka off eBay for $2.95, a Jensen amp for another $5.00 and with the Monster wiring kit, built a 1.2 cu foot sealed enclosure to replace the plastic tray area between the front seats.
Form followed function on the box and the enclosure has the sub firing down onto the van floor, the amp recessed onto the back, and front castors that allow the whole thing to be unplugged and rolled backwards and out of the van. The plastic tray is mounted on top of the box and with matching material cover, the whole unit is pretty much invisible.
OK point I am making is this..the sub sits right beside us and puts out the sweetest softest base you have ever heard...(well, I have ever heard)
The Sub volume control is barely cracked open and it doesn't have to be if you actully want to hear the notes on the base, and not just artilery explosions from the back seat.
It's literally like sitting up on stage, right next to the base player...
I had 6 guys from the Audio Shop jammed into the van listening the system..they all walked away grinning and shaking their heads, the shop forman said they all agreed that this front sub, firing down onto the floor of the van was better than a custom trunk full of subs blowing the mirrors off the car.
My Versa SL came with the OEM Sub built into the back trunk area, and does provide some base back there burried with the suitcases, but for real sound quality, OMG on long trips, do I long for my homebuilt, cast-off, reject, POS $25.00 system.
http://picasaweb.google.com/longo3002
here's a link to my Versa project, use the 'Slideshow' feature to enlarge and auto scroll
Modified by longo at 10:28 AM 12/14/2007