Box tuning and size recommedations

I am now ready to construct my box for my 15'' Immortal subwoofer. I got everything ready , got the MDF 3/4 and now I have a router accompanied by the Jasper iig to help out on the part I always disliked doing with a jig, the subwoofer cutout. I really wish I could find 1'' MDF but evryplace in town does not carry it anymore

I am in a bind of what I should tune the box to and what size I should construct the box internally. People have told me to go by Audiobahns specs and other's have said try 40 hz 3.5 cubes.
The Immortal is meant to be a SPL competition sub , but I have heard account’s of it sounding quite clean in the right box but no one ever knows what size the box was or what the tuning is that they heard it.

I would like to have it pound hard and get as loud as it can while hitting a few lows.

Audiobahn lists 3 different box recommendations and they are: Space saver , Everyday bass performer and ultimate SPl box .
I have built about 5 boxes in my time and 4 of them being sealed and have had good luck but nowwith time restrictions I cannot be making a bunch of boxes until I find the right one.
Here is the link to Audiobahns box specs sheet http://www.audiobahn.com/Audiobahn06/images/tech/2005/boxParams/AWIS_box_specs.pdf

I would like to go with the Ultimare SPL box or around that size.

And here is the subs parameters
Audiobahn immortal AWIS15P

FS 45 hz
QTS 0.493
QES 0.53
QMS 7.21
Vas (liters0 47 liters
Vas ( cubit feet) 1.66 cf
RE 1.3 ohms
LE 2.41 mh
MMD 172.66 grams
Xmax +/-16.5 mm
RMS 2250 watss
SD 0.088 M2
Freq Resp. 20hz-700 hz
Efficiency 97 DB
EBP 85
D 9 5/8
Hole 13 ¾
Displacement 0.7

Any ideas on what I should tune at? I would like to make the ports square using the mdf I used for the box. This is going into a GMC Safari minivan with the sub and ports facing the rear doors. I will be dishing 16oo watts to her.

Any help would be great!

if you want to do a number than tune around 48-52 it should also sound ok box size i would go 4 cubes on 1600 watts need more power for a smaller box less power for bigger box becouse sub moves easyer

Thanks for the input