JL woofers (except the w7) in my experience performed great in really small enclosures ( why they do so well in the stealth boxes)
I did a enclosure for a W6 that sat in the side of a trunk in an IS350. was way small. probably just under 1 cube. with heavy fill, and it still hammered out the lows pretty well.
the hummer H2 stealth box houses a W6 in a enclosure thats quite small.
try and shoot for .90+ with fill and you would be ok.