Here is how I did mine. The back seat is out because I had to pick up a carbon fiber hood for my friends P10 and it fit didn't have to move the seats forward. I love hatch backs.
I had 2 12's in a big box and an amp rack. I used a sheet of wood and traced the carpet, cut it to shape. Anchored the corners and then achored the box and amp to the sheet of wood. Worked really good. I recently removed it and it held up very well.