LOL You seem knowledgable in the subject. One thing with winISD though is its taking into box characterists in a room environment. You could design the perfect box in winISD but place it into a car and your totally off. You can add filters in winISD if youve plotted your vehicles cabin gain, but chances are you havent done that and if your just going to build one enclosure and call it a day its not necessary. In the picture of the prefab box its good the port is offset to the side to use a corner. My only issue with the prefab box is the sub is located in the center. (i understand its for use of empty space and symmetry) but this WILL cause cancellation. If it were me i would use the farthest corner of the cab from the drivers seat as a loading wall. Regardless whatever you build vehicles are difficult to build a perfect box for. Ive been building, designing, and competing for almost 10 years now. Home audio is cake compared to cars