On the Last SL I had- an 87 560SL, I put a Bazooka Subwoofer EL-6 which fit perfectly right behing my drivers seat or you can put it behind the passenger side.

__________________
2001 E55

2001 E320 Sedan

2001 Subaru Legacy

2006 SLK280

2016 Subaru Outback 3.6