I just completed installing an amp under the middle cusion of a 40-20-40 front seat '05 supercab. The usually recommended site...behind the back seat...did not work for me because I've converted the back portion of the cab to better accomodate my two dogs (200+ lbs total). The conversion included removing the back seat cushion and replacing it with carpeted plywood bolted directly to the back of the cab, so I had to find another spot for the amp.

The middle cusion lifts out easily after a sharp tug upward on the front. The space under the cusion was large enough for my amp, although just barely. There are some smaller (Alpine,for one) amps on the market today that would fit into the recess more easily.

There's a safety system module mounted to the floor inside the recess. Rather than mount the amp directly on top of that module I fabricated a simple mounting rack out of aluminum angle iron and affixed it to the seat frame...high enough to clear the module. Removing the seat frame made this a reasonably easy task.

Running the wires was a snap. Straight down behind the head unit, under the carpet, and out of the hole in the carpet already cut for the safety module. The speaker wires run perpendicular, under the seats out to the running boards.

I was concerned about amp cooling, but just finished a trip from D.C. suburb to Florida and back and there wasn't any hint of a problem. That having been said, I was after a cleaner sound (amp and replacement speakers using factory head unit) rather than trying to convert the people in the next lane to my particular music preferences. I don't push the amp very hard.

My thanks to the forum members who reported that wire #2 from the head unit is the right wire to use for the amp relay.

If for whatever reason placing the amp behind the rear seat is not a good option for you, then placing it under the mddle seat cushion makes for a very clean. stealthy installation.

 

What amp and speakers did you go with? How is the sound compared to stock?

What did you use for an amp turn-on lead?

I have an alpine 50x2 amp that I meant to use in my last truck, but never did. It's still in the box, and I've been thinking about getting a new pair of speakers for the front doors. I even have an amp wiring kit that I never opened.

CJ

 

Under the passenger seat works too. I put my MTX sub amp there. It's been then over a year now and I've had no problems with it.

 

The amp I used is a Bazooka EL series I bought over two years ago to use in a '03 F150 supercab. I never installed it...mostly because I never found a place for it that suited my preferences (the '03 had captain chairs, not the 40-20-40 that my '05 has). The speakers I'm using are Infinity Reference Series in the front doors. I chose them because (1) they were relatively inexpensive (I think they may have been recently discontinued), (2) were readily available locally (I was in a hurry to button things up before leaving on my trip to Florida), and (3) when I get a better pair for the front doors these should be fine for the rear.

The sound is much better than stock. Much more clarity. Still too much bass...some sound dampening in the door is probably going to be needed.

The turn-on lead is spiced into the wire associated with the #2 pin on the head unit connector. The amp turns on and off with the radio, including the delay (engine off but door not opened).

 

In my regular cab STX I found that I could put an Alpine amp (older, four channel) inside the frame of my center 20.
It just barely fits.
I had to pull the seat out, partially unscrew one of the side belt bolts, slip the amp in the frame, then put the bolt back down. 9.5 inches wide is about all the room there is inside that frame.
The amp sits to the rear of the airbag monitor. The Alpine does not generate enough heat to be a problem in the space under the seat.

This combined with my Clarion SRV303 powered sub gives me all the sound I want in the regular cab, while not giving up any of the functionality.

That center seat is not much use as a seat, unless you are transporting smaller children.
Chris