You dont have enough air space for a 4th order or 6th order for 8 12" subwoofers. You MAY be able to get a regular ported enclosure in there, but I doubt it.
Also consider complex box needs a lot of wood. Every sheet of 3/4 inch wood you use = 2 cubic feet, bracing will take up volume as well. I would say just the wood and bracing for a box big enough for that many woofers will be 6 to 7 cubic feet!
I think you may be able to do them in a regular ported box. Really I would advise against bandpass for such a large build since it will be very easy to get wrong and very permanent.
//content.invisioncic.com/y282845/emoticons/crying.gif.ec0ebefe590df0251476573bc49e46d8.gif Instead we think!! i wanna mount 8 12"!!!!!! help me!!!!! //content.invisioncic.com/y282845/emoticons/*******.gif.a649d21efc0d1fd4890a6428166586c1.gif