The bad news is that despite its low Fs, this driver starts to lose its excellent 90dB efficiency under 100hz..
The good news is it's pretty forgiving without "heroic" enclosure efforts. This will be an easy enclosure to tune, the following specs will give you a -3dB point of 26hz and excellent linearity (+-1dB within your pass band, rising gently to +2dB above 140hz) and a -12dB/octave linear roll-off below 24hz (set your subsonic filter, if applicable, for 24hz)
Box: 2.6 net cubic feet volume Port: 3" diameter, 9.25" depth (flared both ends min. 1/8" radius)
Alternate port: two (2) 3" diameter ports 20.6" deep (flare not necessary, but OK - includes compensation for no flare)
Alternate port: two (2) 2.5" diameter ports 14" deep
Alternate port: 1" x 13" (rectangle) 16" deep.
Minimum port (must be smoothly flared, like 1/2" radius or it will whistle) 1"x6" (rectangle) 7.2" deep
Enjoy your project!