I tried the Bose Bass FAQ and found that it cut out too much bass for my taste. So here's mine.
Parts needed (from www.partsexpress.com):
Qty. 2 Audax HT170G8 6.5" DVC Subwoofer (296-99) @ 31.90 ea.
Qty. 1 Cascade Quite Kote Damping Spray (268-250) @ 16.90
Qty. 1 Dynamat 2 SQ. Ft. (268-095) @ 9.95
The 290-250 speakers are 8 ohm, the original Bose are 2 ohm. That means that they will draw 1/4 the current that the Bose will (ohms law), the Audax (I know French Speakers in a German car) are dual voice coil subwoofers, two 8 ohms. You must first solder wires + to +, - to-, to make them 4 ohm (1/2 the current draw). After that its pretty much the same as the "Bose stereo bass" FAQ.
1. The speakers are 6 13/16 not 6 1/2, so you must trim the opening behind the grills on the under side to accomondate them BE CAREFULL, the screw holes make a diamond pattern with 1 screw hole pointing towards the front, other wise the mount just fine.
2. Spray the underside of the shelf with the damping spray, at least 4 coats. Do not spray the padding just the bare surface in the area between the grills.3. Cover as much bare metal on the fixed shelf with the dynamat (cut with sissors). DO NOT cover the openings as they let pressure out of the trunk when you close the lid (if you don't believe me watch the speaker cones move up when the trunk is closed). If the pressure relief is blocked you can damanage the speakers from excessive movement. So do not stuff with any material. The spray and dynamat will try to do the damping.