There is a thread about a pricey fiberglass dual sub box that also mounts an amp.
Custom fiberglass Sub box and Bezel pics
It looks nice and the price is not that bad when compared to paying an installer for alot of hours to make a box.
I was thinking about getting that box, but I have 2 amps and only used one sub and I wanted to keep the space open under the passenger side rear seat for storage.