Wow I thought I was the only one on the forums with that car.
We have the same car. Mine is a 95 w/ 22k miles.
I took my spare tire out, and have batteries down there. MDF floor built over it to flatten everything out.
Heres my latest idea..
Car Audio Classifieds
Almost 6 ft^3. Box will be built inside the trunk, and will be the WHOLE trunk. I will even have to make 2 spots in the box like slots/cutouts for the trunk hinges.
It will be loud though
The last box that bigdogjk has a picture of is the BIGGEST box you can fit into the trunk and still remove. I spent a long time getting those measurements correct, and I promise you cant fit anything bigger w/o building it inside the trunk.
You actually have more height than you think you do. If you stay far enough back from the trunk hinges (make sure to account for where they move up/down) you have 13+". If you dont believe me, climb in the trunk and have your friend shut you in there with a tape measure like I did. haha