You’ll be hard pressed to find a 10” sub that will fit under the seat in a square…
This is a 13.5” shallow mount but was just a little too big to fit behind the seat and have the seat go all the way back without making some modifications to the seat frame.
If you build a box for a shallow mount 10” you should be able to get the appropriate air space (box volume) and get the seat back.
One trick is to build the box narrower than the vertical bars on the seat back, this allows the box to kinda press into the seat back. I made this box full width causing it to hit the seat frame necessitating modification of the seat.
Another way to get the seat farther back is to angle the box to match the angle of the seat back. Also, max height can only be about 14” before the box hits the bump on the back of the cab.
If you’ve got money burning a hole in your pocket Sloshtubz sells really nice looking custom speaker boxes for the square body’s
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