In my hatch I had 2 10s on 800w (bridged) at 2ohms. They sounded best when they reflected off the rear glass and back into the cabin. In a regular car. I've always heard/felt the best/strongest when they were faced towards the back. Even in my buddy's sedan with two 12" JLs in a ported box that took up his whole trunk, they faced rear. You'll have to flip them around and figure out which is best for your sound.
Dunno what to tell you to do about the rattling... I shook my hatch loose by using my subs all the time.