I installed a touchscreen pioneer double din with the am to fm antenna adapter, so the antenna doesn't pop up anymore and make my car look like an rc car..
Also put 4" infinity reference speakers all around. Had the 6.5", but didn't know about the speaker pod adapters at the time, so I returned them and got all 4".
Those didn't have any bass whatsoever, so I built a box for a single 10" infinity reference sub. I did a lot of research, and built a pretty simple box.
I never took pictures and I can't remember the dimensions, but it fits perfectly below the targa when I store it. Did an angle for the back of the box to rest against the rear seats. Has over the minimum space internally. Built with 3/4 MDF, glue and a nail gun. Bought a giant roll of "outdoor carpet" from a hardware store and covered it. Actually turned out really nice. Nothing professional, but doesn't stand out or look like a best buy pop-up box.
I may have overdone it by hooking it up to an 1800 watt Kenwood amp with 0 gauge wiring, but I had this amp set up to 2- 12" kickers in a huge ported box in a previous vehicle, and this single 10" hits damn near as hard as they did. Perfect setup for me, and I love the reference series speakers. They all sound so clean and crisp, including the sub.