Right now I have 2 10" Punch DVC's in a ported box in my trunk. The ports kick the air out of the sides of the box and the subs are facing backwards. Needless to say my trunk lid rattles like a mofo even with 2 layers of dyanmat. I took out the rear deck speakers to use the holes like ports. I get louder bass and less boominess, but the trunk still rattles. Now, ideally a box with the ports firing directly through the holes in the rear deck would be great, and I am guessing even better if there was a seal so no air went into the trunk, but since I don't feel like spending an arm and a leg on another box I was thinking of this. I'm not sure how this would sound or if it would degrade the sound at all but..If I could somehow have PVC coming down from the holes in the rear deck, with seals around them so the air went no place but directly into the car, then rig an elbow and attach the PVC to the ports on the sides of my box (with seals again) esentially routing all the moving air into the car and allowing the least amount of pressure in the trunk to rattle my lid. Let me know what you think pro's and cons. I REALLY want to try this but would like some insight to how cool it would be.

I had an old Cerwin Vega Subwoofer manual that showed sheet metal tubing (instead of PVC) venting through the rear deck from a ported box.

your existing ports inside the box are supposed to be a specific length and diameter that is specific to that box. If you add length to the ports by extending them up to the deck, you will effect the tuned frequency of the box and you might adversely effect the performance. And unfortunately, ported boxes are not as forgiving when you stray from the original design. So what I'd do is remove the existing ports from inside the box and try to design the new ports so that they are the same length and diameter as the original ones... except they will be outside of the box as opposed to inside the box.

Let us know how it works.

Ported boxes are very .... difficult. It's hard to get the right volume and accurately port the box to get the right frequency and so forth. When you add more holes, simply more air is let out, and there is a greater volume...meaning your subs might not sound as great as they could. Most subs work within a small recommended volume range, so if your box has the correct volume now...it wouldn't if you added mor eports. I'd recommend sealing up the other ports in the box, because you would just be making the volume greater. And, if your volume is correct with the ports you have now, making the ports on top the same size would logically give you the same volume that you have now. It's hard to calculate the volume with a ported box, and adding new ports screws everything up. And also, you would most likely end up Dynamatting the entire rear deck and PVC pipes to stop them from rattling too...