0.66 is
entirely too small for 2 12's and even 2 10's

, that doesnt even account for the displacement of the magnet. There's only volume enough for a single 12". Furthermore, it's using 5/8 MDF which is far below par since there's 1/2" available. This box wont really, significantly, reproduce any bass reinforcement much under midbass frequencies. Not to mention it'll make this
annoying rattle from your midgate.
This is not necessarily true. I'm about to purchase a similar box from another vendor. Same design but it offers .7 cubic feet per chamber. The Rockford Fosgate shallow mount 12" calls for a minimum enclosure with .6 cubic ft. The minimum their shallow 10" calls for is .4 cubic feet. Saying it is too small for 12's isn't correct, saying it's even too small for 10's is even more incorrect. Remeber that measurement is per chamber, not total. And why is 5/8 MDF inferior to 1/2?
Not to mention you could, (and I will) add polyfill to the enclosure as it is on the small side.
In preparation for my Avalanche to receive this enclosure in that location I have also separated the trim from the midgate and deadened the whole thing with butyl tiles and closed cell foam. My midgate feels like a heavy wooden door when I pound on it with my fist.
I haven't found much on this box on the forum and am looking forward to trying it. Should make for a clean and easy to remove install. I also listen to rock and metal so really don't require a big ported ghetto blasting box.