I like the sound of this subwoofer, and it is easy to add to any system.

http://www.cardomain.com/item/INFBASSLINK

It is sealed, but has a passive radiator. It has a built in Amp with auto-on, and several mounting options.

The folks at this link will get it to your house for $255. They are authorized Infinity. (I have no affiliation).

Crutchfield and Circuit City (both Infinity Authorized as well) sell this same item, but are charging over $300 with shipping.

A great way to wire this in to your system is to build a breakout harness by buying the "into car" harness and the "into radio" harness, then splicing the runs to the L+, L-, R+, R-, and the remote amp wire back the speaker.

Metra makes a breakout harness just for this purpose. It's part number 60-7712.

If you want only one end, the "into car" end is 70-7712 and the "into radio" end is 71-7712.

The amp signal wire on Isuzu factory radios is one of the two unused locations. I honestly can't remember which one it is, but only one of them provides power when the radio is on, that is the one to use. My aftermarket amp is signaled this way. You will need an extra pin for that location, you can buy a second "into radio" adapter and move the pin from one connector to another. You may be able to get one from the Isuzu dealership. Toyota Part number 82998-12340 is an exact fit for this pin; you'll have to order it from a Toyota Dealership.

An easier way to install the unit is to splice locally at each rear speaker for the L and R and use the "auto on" feature of the speaker to avoid running an amp trigger signal. It may be possible to use the antenna amplifier's signal wire, but that's only if the antenna amp is nearby in the vehicle, you are comfortable splicing into this wire (noise worries, etc) and I am uncertain if this wire is powered when the radio is not playing (like when the CD or tape is playing).

Good luck! I make you no promises, let us know how it turns out.

Nate