Currently, there are no "slim" boxes available, that I'm aware of. Tech12volt (a site sponsor) is working on one for under the front seats. The system in the Titan isn't easily expandable unless you add an LOC or additional amps. I have a single 10" in a tech12volt box under the rear seat and it ROCKS!!! The 8" stocker just isn't capable of hitting the required bass for the most part. I don't even know it's on anymore. You may want to hit tech up with some questions and see if you can get 2 new boxes and amps for under there and replace the weak stocker. It'd definitely be worth it. :thumbsup:
And welcome to the site!
And welcome to the site!