Size of boxes

Wow you are in luck, I used to be an Audiobahn dealer. Designing sub enclosures is my fulltime job. So here you go.-
If you are looking for sound that is very smooth, and has a very low end shaking everything setting off car alarms. You will need a PORTED BOX that is 3 CUBIC FEET FOR EACH SUB WOOFER. It actually calls for 2.7cu.ft but after you add speaker displacement and bracing it should be at least 3 cu.ft. The port can be either round or square made of plastic or 3/4" wood respectively. My port suggestions are dependent on how much space you have. The shortest round port might make some noise (too much pressure!). So think about that first. Anyway the short port is 3" diameter and 15.5" long. The longer port is 4" in diameter and 28.25" long. The rectangular wood port can also be either (port measurements are inside diamensions) 3" w x 3" w x 18.5" long (short port) or 2 w x 10.5 h x 48' long. The second longer wood port is recommended most but will take up a lot of space. The fact that you have to subtract the port volume from the box makes for space issues in cars. Also the second wood port sounds better and won't make much wind noise, but takes up .75 cu.ft worth of space. So in plain english your box will have to have an internal volume of 3.75cu.ft. An example of this could be made of 3/4" thick MDF, have 1" x 1" internal bracing and measure (box dimensions are external and assumes the use of 3/4" MDF) 12" h x 18" w x 30" deep. The port is an integral part of the box fitting inside. I'm sorry I can't provide any drawings to make things easier. Now this box size is one that I ran through a computer program I use. So it is not the same as the manufactures recommendations. I will list those as well.
The second box is an example using a round short port and also uses 3/4" MDF, 1 x 1" bracing, the 3" dia x 15.5" long port, and measures 12" x 18" x 24" externally.
If space is an issue try checking out the information below. -I got it from Audiobahn-
If for some reason it doesn't show up or you need assistance let me know. Good luck and enjoy your new setup-I'm sure you'll be happily disturbing the peace soon!
-Dynami
Model # AW1006T
Ported
Air Space (Cu. Ft.) 0.65
Port Size (Inches) 2 x 6.5
Port Vel. (%) 48.31
-3dB (Hz) 31.5
Tune Freq. (Hz) 40
Sub Disp. (Cu. Ft.) 0.21
Port Disp.(Cu. Ft.) 0.01
Total Vol. (Cu. Ft.) 0.75
Ported
Air Space (Cu. Ft.) 1.4
Port Size (Inches) 3 x 6.75
Port Vel. (%) 24.19
-3dB (Hz) 30
Tune Freq. (Hz) 39
Sub Disp. (Cu. Ft.) 0.21
Port Disp.(Cu. Ft.) 0.024
Total Vol. (Cu. Ft.) 1.5
Ported
Air Space (Cu. Ft.) 2.4
Port Size (Inches) 4 x 6.25
Port Vel. (%) 14.39
-3dB (Hz) 29
Tune Freq. (Hz) 39
Sub Disp. (Cu. Ft.) 0.21
Port Disp.(Cu. Ft.) 0.04
Total Vol. (Cu. Ft.) 2.5
EBP 74 80 80

Sealed NR NR NR
Minimum (Cu. Ft.) 0.5
Maximum (Cu. Ft.) 1
SPL (dB) 80
All sealed boxes already include the displacment for the subwoofer. NR = (Not Recommended)

add 2 inches for the height , add 2 inches for the width and add 6 inches for the thickness, that would be minimum, to optimize the power of subwoofer additional 4 inches more on the width, your reference is the size of your speaker, use divisions instead of a ducted pipe.