If my calculations are correct, that results in a 214L enclosure before you subtract driver and port displacement. Have you taken a look at the Tempest applications files on the Adire website? It tells you everything you need to know.
If you corner loaded it, you'll come close to the mid-20's, but with authority and a shallower dropoff in the bass, and you'll get a little bit better (tighter) transient response for music. (Of course, this is making the best out of the given volume constraint).
Pete Mazz loves his sealed Tempest subs, he's got 2 of them, each in around 5 ft^3 sealed enclosures.