here is a guy who took the whole back deck out...


maybe if you make some speaker pods to hide the ports in the back deck it might looks ok....

 

Worst comes to worst you can just pick up a new deck lid at the wreckers.

I have a 2007 Cobalt SS/SC and I wanted to do something like this, I have so much sound damp. material back there its not funny but the deck lid still rattles.
I wanted to run 2 ports through the stock speaker locations but not have the ports meet up with my box, just want to give the air someplace to escape into the cab of the car so it won't put so much preasure on the deck lid.
Damn Cobalts are rattle factorys

 

I took mine out and rebuilt it to look like a factory one, but without the rattle factor.
I fabricated special ported areas to allow the flow of monster air to be introduced into the cabin area. I can get a 142 on the TL before my deck skips.