Having done several upgrade audio jobs on my wagons I can tell you a little from my experiencies:

1/ On my S123 300TD, which came with the rear facing seat, I installed the amp on right hand side of the front dash console (passenger footwell, on the outside: vertically screwed to the carpet lining). In Europe, most M.B.s install the cellular phone at this point, so it actually doesn't look weird.

2/ On the same car I had a handmade subwoofer system installed to the back of the middle seat, anchored by Velcro to the rug. If I lowered the middle seat, I could move the subwoofer box out of the way pretty easily.

3/ On an S124 300TE I did installed the subwoofer (handmade also) on the middle hole of the spare tire. The cover had a special opening done keeping the original carpet, so sound would go out but the cover would look the same.

4/ Finally, on my E 320 T, which did not come with a third rear facing seat, I had the amp intalled in the rear most compartment besides the gate. It works fgreat. If you do not use your third seat often, I would buy the regular cover from the dealer and exchange it from the one that has the bottom part of the seat. That will provide you with more space in that area. Keep the original so you can change back to the original setup whenever you want to.

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A. Rosich
CL 500, 1998
S 500 L, 1998
E 320 T, 1995 [Sadly sold ]