Hey John,
Just to get the ball rolling on this discussion, I'll tell you how I plan to try mine at least for the first try version.
I'm putting two tens and one eight on my wall, facing forward. In order to keep it simple and cheap and not time consuming and labor intensive, I plan to buy boxes on
eBay for each woofer, and simply tack them to the back of the wall.
Unfortunately most ported boxes are ported in the same direction as the woofer faces. I'm quite sure that a port facing forward will have very little benefit. In my experiences, ports and preferably woofers must be facing something off which to reflect. Following this logic, a woofer facing the front is a sub-optimal configuration if housed in a simple box. I want to do this wall thing regardless for cosmetic reasons, and I will already have two twelves in the trunk. But as far as ports go, I would prefer to install them because I do like ported boxes. And they should certainly face downard I would say. However, porting a sealed box apparently requires quite a bit of science. I don't want to screw up the port job and end up with what I have heard called 'a leaky sealed box', or one with 'port noise'.
On another note, this whole wall thing with woofers facing the driver is getting popular as you mentioned. I went to a local car show here in Orlando and a number of vehicles had this configuration. Back then I was unfortunately not planning to do this, and did not get any information from the guys who did it. I would imagine however that the results must be strong as you mentioned, otherwise people wouldn't be doing it. But in order for it to be successful, I do think that a complicated all encompassing enclosure that basically turns the 2nd to last 1/4 of the vehicle into a speaker box is necessary. Oy, I'm just not up for that I don't think. Maybe on the 2nd try. I want to try my simple version first. Hopefully 2 twelves in the trunk, 2 tens and 1 eight on the simple wall will be enough to satisfy the first time. I just don't have $1000 to throw at the local shop to design some kind of super custom scientific box for my vehicle right now.
Well, that's where I'm at thus far. Right now I'm going to go out to the local auto parts store and stand around for a whole fvcking afternoon so I can get a couple of bolts to put my front seats back in (car is gutted, has been sound deadened extensively) and see where exactly this wall will fit into the vehicle in relation to the front seats fully reclined.