I was going to use those subs and had worked on a box for them. I found a box that was 3.5 cubes, that used a single slot port (12.5" tall x 2.5" wide x 17.5" deep) worked well. Combined with a subsonic (infrasonic) filter set at 25hz and 12db/oct, it tuned the box to 33 hz, and had a port velocity peak of about 82 ft/s @ 30hz with 1000watts. It had good group delay, and cone excursion was under xmax at all frequencies. Spl was above 120 db from 40hz-80hz with a smooth frequency response. You can use any dimensions you want as long as the box volume is the same and the port opening area (31.25 square inches) and length (17.5") are the same. Alternatively, 2 round ports 4" diameter x 14.5-15" will be about the same.

 

Thanks so much! I've got a real good idea of what I'm going to do now.
I'll try to post my design and take some pictures as I build it.
Hopefully it's just as loud as I want it to be!

 

I've designed the box using Rhino to spec. heres the renders!
Note: The top piece that hangs over is not to spec, i left it long, because i want to cut it so that it will fit perfectly

 

files are attached here