I have to disagree with just a nuder...
Sealed boxes are great in many applications. In your f-body, space is of major constraint, especially if you still want to store your t-tops in the hatch cavity. A sealed box can sound great if built right, with no air leaks and proper bracing. Ported boxes are more efficient, naturally. But it's possible to play a speaker as loud in a sealed box (assuming you can build the box big enough). A speaker's SPL limit is a function of cone area x displacement/stroke, and that limit can be equally reached in a sealed or ported box. The only difference is at what frequency you reach your SPL limit. Physics, plain and simple. Speakers are mechanical devices, and follow those rules of physics just like anything else.
And as far as box shape goes, it has been repeated over and over and over that it's best NOT to build the box as square as possible. The standing waves created from the back wave of the woofer create artificial harmonics and can "tweak" your speaker's expected frequency response in a given enclosure. If you desire "one note" bass, you may desire the bump in your frequency response that those standing waves create (assuming you actually know that frequency and tune to it.)
And yes, again, it DOES matter which way the box is pointed, sealed or ported. A subwoofer system in anechoic space (large room with no "live" walls to reflect the sound and create nodes of peaks and valleys) will sound the same no matter what direction it's pointed. But in a car, ANY CAR, there is something called TRANSFER FUNCTION, wherein the vehicle's internal airspace and shape play a big factor in how much your bass/sub-bas output is extended, and at what frequencies.
Sorry if this got a little technical. I just want to stop the baseless drivel being spewed. This is why I enjoyed working in car stereo for so long. People who do not understand the physics involved in desgining speaker enclosures and how they will interact in a specific vehicle or environment make claims based on "experience" or subjective opinion. I have been able to take customers from good to great by simply tuning and tweaking their current setup. Books by Vance Dickason and a simple MECP installer guide book can do a lot for someone interested in car audio who may actually want to learn something before they go talking crap.
To answer the question again to the original poster - if you'd like help with your custom enclosure, please email me direct at
erikquick@yahoo.com. I have done enough f-body subwoofer systems to help you run down your options based on your needs/wants.
Thanks!
Erik