[Roy Batty]

The place I want to put the box has a max dimensions of 48" wide,
10.5" high, and 7" deep. So these are the limits of the outside
dimensions of the box. Can't make it any larger without it getting in
the way. It's going to go under the front edge of the rear couch. If
it is any deeper, people's legs will rest on the upper corner.

I had my heart set on four 8" woofers which require 0.55 cu ft each.
Two will be on one side, two on the other, with the enclosure walled
off in between the pairs - the amp driving these four woofers
(Panasonic CY-PA2003U) will have each side driving a pair of woofers,
and a 6x9 (one on each side, mounted in the wall just ahead of the
couch). The front part of the van will have its own amp, same model.

Problem is, when I do the math for a sealed box, I come nowhere near
the 1.1 cu ft per side that each pair of 8's will need. I might get to
0.89 cu ft per side depending on what board thickness I use, but I was
hoping to use 3/4" MDF. Would 1/2" thick MDF be feasible?

So, it comes down to a ported box if I want to make the available
space work. This port calculator page I found seems to require a port
length that would simply not be possible:

http://www.carstereo.com/help/Articles.cfm?id=31

With two 8" woofers, and a tuning freq of 30 hz, the first part gives
me a port diameter of 3.46".

Entering this value into the Vent Length calculator, keeping the
tuning frequency at 30 hz, and the enclosure volume at 0.89 cu ft, I
get a Vent Length of 29.1 inches! Bah!

Is it simply not possible to vent a box that small?

On the other hand, a sealed box that is 20% smaller than it should be
- is that necessarily a deal breaker? Doesn't it provide some measure
of safety against cone overexcursion? Will it really be taking that
much performance out of the woofers? Will it be "good enough" is what
I'm getting at, I guess.

Thanks very much for any insight!