Its a dual 4 Ohm 12" sub. The enclosure is about .9 cu. ft. sealed after the sub displacement.
I usually just do a box from MDF but wanted a more permanent and less intrusive install in my WRX. It took me a couple weeks to complete with all the other stuff going on but I am very please with the final result.
Its secured by the recess in the floor of the trunk and the bolt through the back of the enclosure that attaches to a stock mounting hole in the side of the trunk as seen in the pic.