I have calculated an enclosure for the SD-12 for a user of the forum and wanted to post the results here as well for others to utilize if needed. I have to mention first that this particular driver will have higher efficiency in a ported style enclosure, but is good for sealed as well.
Here are the specifications:

Double Baffle design

Volume:1.46 cubic ft
Recommended tuning: around 47-49Hz (material dependent as well)
Note: Golden ratio was used for enclosure physics
Mounting depth: 10 9/64"
Cutout diameter: 11 1/8"
Top baffle cutout: 12 5/8"

External dimensions: 10 57/64H, 24 3/16W, 15.5D
Internal dimensions: 8 41/64H, 22 11/16W, 14D

Here is the picture of the design:



Enjoy!