How to install an amp under bench seat?

I bought a 03 Silverado Ext. Cab a couple of months ago. I wanted to put some subs in it and I happened to come across the prefect setup for me. I was wondering how did this person mount the amps right under the seat. If you all have any suggestions I would greatly appreciate it.

Most likely on the center hump in between the subs

Looks like they did some modification underneath the seat. I have an 01 Silverado Ext. Cab and there is planty of room behind the seat on the rear wall to mount amps (that's where mine are). There is close to 3-1/2" of clearance between the seat and the wall. I'm assuming the 03 hasn't changed much in regards to the seat.

I have an 02 Silverado. I was going to try and mount amps on the back like kklagge is saying but, when you fold the seat up the seat goes back and area was a little too small putting the heatsink too tight against the seat. I also had a goal of not putting any new holes in the vehicle which I was able to accomplish by putting my amps on that center hump mounted to a sheet of mdf covered in matching carpet. Crutchfield sells boxes similar to what you see in the picture and they have what they call an amp rack in the middle. Check em out at crutchfields site.

You must have a pretty thick amp if it wouldn't go behind the seat...when my seat is is lifted up the back actually stays the same distance from the wall as it is when the seat is down. I have a custom box with dual 12's so there is no room on the hump for anthing else.