I have the underseat tool box in the back at the moment. The mods and highs do sound good in the truck but the bass is either not handled well by the speakers or stuff just isn't rigid enough. I hear vibrations or something and to me it sounds like the speaker bracket inside the door isn't solid and is flexing when the speaker hits. When I used to built sub boxes I always always always made sure they were solid as hell, and that helped with clarity a lot.
Any way I'm not real impressed with the toolbox, but it does keep the truck cleaner. My stuff isn't rolling around anymore now that I have the box. It's a lot smaller than I hoped it would be. I suppose I could do without it.
I definitely think an 8" would be more than sufficient for my needs. Hell I like the bass that comes out of my 5" Klipsch speakers in my living room

but that's all design and efficiency - and a large case as well.
How do I wire in one of those mtx subs with a factory deck?