Good luck with the feeling it outside your car for $300. The amp for my subs cost $300 by itself and I only pull 135db which is barely loud enough to annoy people outside.

DONT buy Sony - they are nowhere near accurate with their power handling claims. The "800w" amp actually puts out 125w RMS into 2 channels.

You are shooting yourself in the foot by getting a box that spans the entire rear of the trunk - you are cutting off the passage of air to the inside of the car which will definitely hurt your volume.

You can build a fiberglass box that sits in the wheel well and fires INTO the cabin for less than $100 if you have the tools already. That will be louder, cleaner, and lighter than an mdf box.