Well, here are some pictures (only one at the moment, I'll get some more pics later today and edit up the message) of the empeg install in my beetle.
cambscar did a very neat job of the amp & sub (Kicker 405 - 4x40w+1x240w/Phase linear 10" flat subwoofer) including making a very neat & small box which means I still have some room in the back!
The amp is fitted to a carpet-covered wood mount, not the back of the seat: I can still fold the seats and the wires are all run under this mount, and the whole system can be removed without marking the car. There's the remote subwoofer gain control hidden under the dash too!
Hugo