I installed my subwoofer box from my 2006 convertible into my 2012 convertible.
The box had to slightly modified to fit, as the '12s have more reinforcing in the trunk area. A 1/2" high notch had to be made. Also, the back is VERY tight, I almost shaved a slight taper into the passenger side bottom rear/side of the box, but this fit OK.
The installed box leaves plenty of useable floorspace... 22"+ deep and the spare tire more accessible in an emergency than those huge boxes that are bolted to the floor.
The subs are simple 10" Kenwoods. It won't cause earthquakes, but it fills in the Shaker 500 sound nicely.
Here are some pics... hope this helps!