We tested it with his hertz gauge thingy and it didn't touch on a carpet sample. I though I would install some of the speaker spikes to one insure no movement and two just a little more distance between carpet and speaker.
That speaker will move .65" in one direction max, according to JL's website. So it'll probably be close. I'd space it up about another 1/2" to be safe. You don't want it hitting anything or you'll be buying a new woofer sooner than you'd like.
Box is made of MDF board and it's 3/4 thick material The Line-X guy charged $75 and its a hard sprayed on truck bed liner. The box is 300 bucks and custom built in Buford Ga by Performance Works Ph.678-714-4559. They charge $400 with a subwoofer. The box feet are 1.5 long and the excursion is .65 or a little more than a 1/2 inch. The center won't come past the foam because I am only using a 400 watt JL a1400D amp. I think if I had more power it could be a problem but I'll look this weekend.