if it was a CRX, I'd tell you to just mount them in the floor behind the seats, facing more backward...
In a hatchback, you'll usually get the best sound if the sub(s) is/are pointing toward the center of the rear window, as you get the "echo" effect..
You won't hear the sharp "tinging" or "metallic" sound that most subs make on hard notes, and you won't notice reverb from inefficiencies in the construction of the enclosure.
Remember in the enclosure to use matting, so you don't get interior echo from the air pressure in the enclosure.