I just finished installing a new audio system in my 2003 F-150 Lariat, which included an Alpine cassette/cd changer, along with a 5-channel amp, XM and Alpine component speakers throughout. I was hoping that by going with the Alpine component speakers throughout, I could avoid the problem of subwoofer installation/location. Alas, no dice. The system has awesome mids and highs (installed the tweeters in the side doors near the sills), but lacked the "thump" that I was looking for. Against advice of my local audio parts retailer, I ordered a (non-powered) 6" SAS Bazooka base tube from Crutchfield. It fits under the passenger-side seat like it was made to be there. I installed the 5-channel amp (so didn't need another amp) and changer under the rear drivers-side seat. I'm not sure that the powered base tube would fit, but the unpowered was perfect. Of course this whole operation took 4 consecutive weekends, and cost $3k+, but what a difference! If anyone wants details or pictures of the installation, let me know and I'll dig out the digital camera! Thanks!