In considering the design for an audio system in the STI, I’ve come across of a couple of pretty slick items. Space is obviously a concern, since having a trunk means learning to use the trunk. Fiberglass is obviously a nice choice considering the reduced weight compared to wood. Audio Integrations makes a couple of really slick items for the car:
The pictures below are from the manufacturers site and are not my car. Pretty sweet items if you have a Subaru that they fit inside, light weight too.