new box ????

[slow240sx]

I got a dd 9515, gettin ready to build new box this weekend. 1992 240sx hatchback. Biggest total box size is 6.0. Will have to do sub up aiming @ hatch glass. Where should I put port. Can't rear fire it cause box goes all the way back of car. If I made box bout 5.0 I would have bout 4-5 inches from rear of car and I could rear fire it. What bout putting round port on side of box towards the rear. There is some unused space there for the port to breathe. My box now has sub and port up but with the fifteen I won't have enough room to put it up. Do slot port get louder than round pvc? I was thinkin of doing pvc for now to see how I want it tuned and id b able to adjust it easier. Lmk some suggestions.