How about under your front passenger seat? I never used the lock box, so I just took the box out and put an amp and navigation brain under there. The pictures below are before the removal of the lock box and when it was still sticking out a bit into the rear passenger footwell. I actually moved the amp and nav brain further beneath the seat. Now no one in the back seat can kick or see it unless you move up the front passenger seat. However, it was a pain in the bum to run the wires. I suggest connecting all the wires to the amp with some slack, then place the amp under the seat and then just pull on all the wires to remove the slack. It's a pain in the bum, but it gives a nice clean look, well at least when you have your front passenger seat moved forward.

