I just did the World Dodgiest Install and put my old amp on the floor behind the passenger seat and my old sub box in the boot:

Sounds kinda noisy and crackly due to the **** amp and really, really **** LOCs I got from Jaycar. But, it still sounds a million times better than before. The HSKs now sound as I remember them, nice and warm with midbass that really kicks. And having a sub again is awesome.

I haven't had time to tune anything properly yet. Any suggestions as to x-over points? 6.5" splits up front and a 12 Blau sub in a sealed enclosure.