I'm a little jealous...was trying to do this in my truck with a 1500w (or 2000w?) but there was absolutely no place to mount it, except for the rear floor like he did. I wasn't willing to give up that space.
I also would never hook a 3000w load directly to the back of a modern alternator ...scratch that...ANY alternator, but that's just me. I also wouldn't use a 3k invertor with the engine running (on a computerized vehicle). That's a heck of a shock load.