Shouldn't be hard, I got a 5 cube box in this GA with room to spare (trunks actually a few inches smaller than a cavi too). I aimed my in cabin, and fold the seat down when I'm in, and its nice. Angle the face so it's 19", and drop it in like that
edit:
Yea i know that window prob... Some silicone fixed that //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif
and I had to saw-zall the rear deck out to the 6x9's to get the box in, take back seat out, and one front (wouldn't go through back door). But once it was in (wasn't that hard, just heavy), i could've made a bigger box.
I just contemplated putting a 18 in here (facing the rear deck, I'd cut the rest out though), same one actually, but decided against it.