better yet get some tow straps and cut a hole through your roof and strap it down where you cut the whole so it faces into your carStand the box up on it's side and put it in the front passenger seat... buckle up.
I had my sub box in between my front seats once...didn't sound anywhere near as good. I didn't play around with the aiming at all either, so that might have changed something.the front seat would be dope