I'm getting very exited about an idea for a sub for my SL, and thought I would share. It seems like the trunk is very well sealed off from the passenger cabin (gas tank and steel bulwark), plus it's very small to begin with and I would like to save some luggage space.
Right now, I have one of those 'kinder seats' (came with the car) that really aren't big enough for an adult, so it's going to go in favour of a custom storage space.
Not having seen, except pictures, how the original storage area is constructed, I'll assume a plywood panel on the bottom and one on the backside, both carpeted. What I'd like to do is set up the sub so that no matter what is in the storage space, the sound from the speaker will never be covered. That eliminates the 'floor' panel and rear panel (if it were built out from the backside).
I want to use one of the newer shallow sub designs that require only 2" - 3" of mounting depth. That should allow for 1 12" sub mounted on one or the other side of the 'floor' panel, with a total enclosure volume of about 1 cu.ft utilizing the entire back 'seat' area/depth.
Then, I'll make a panel to cover the 'seat' area, looking just like the original with carpet, but mounted about 2" over the panel that the speaker is mounted on. I'll make a grille on the front side, across the width of the back, again about 2" high, so the sound will always be exiting forward.
I'll loose only 2" - 3" X the depth X the width of the rear storage space, the speaker will never be covered with luggage, and will be almost completely hidden.
I'm not sure what to expect with the bass firing into a 5 sided box, with one side only 2" from the cone surface, but it might just work. Comments?

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1986 560SL
2002 Toyota Camry
1993 Lexus