Adding small Sub to 2008 Reg Cab SR5 4x4

Hi,
I've got a 2008 reg cab 2.7L 5 sp reg cab 4x4 SR5. Wife just bought me a nice JL Audio Component Set for the front doors and a nice Kenwood to run those.
I finally got it all wired up New Year's weekend and it sounds great. Then, I had back surgery on 04 JAN so I'm not going to be doing anything with it, specifically driving, for at lest another 3 weeks.
I found a nice JBL GT4-A604 amp on harmanaudio's store (bought my voice matched jbl northridge's 5 years ago from same store on ebay) for $52! Wow.
So, now I want to use two channels to power the door speakers and bridge 3/4 to drive a small sub. I know a 6 1/2 bazooka tube will fit behind the pass seat w/out impeding travel and if I put amp under pass seat, it'd be an easy wire job. I've never bought a sub, I don't want to shake the windows of the cars next to me, I just want to balance a nice sound from some good components in the door, and have a little bump. What are my other easy options, besides building buying a complicated box?

THanks for the help!


Love my Taco!!!!!