The Tempest-X can be used down to 3 cubic foot sealed. Fill it with poly fil, and you'll be fine. I will say i've got 2 of these subs with 600wrms each and they're producing insane amounts of bass at 30hz and LOWER. I actually had a test CD in with 15 hz.... lots of vibrating, but inaudible. it felt like someone was outside rocking my car back and forth. The subs itselves were pushing 2.5" of excursion peak to peak. Shiva-X should provide similar results... just not as much.