one 12" in a sealed box will pump enough bass in to your car for you to hear, that will be clean, and it won't be thumping. In my W124 I have a JL 12W3 in a sealed box in my trunk and I get plenty of bass in to my cabin. I wouldn't worry about porting it by cutting your rear deck or anything. If you're looking for thumping bass, then you might wanna port it in to the cabin. Since you're not, it should be fine.