Has anybody here added a subwoofer and amp to the factory head unit setup? A shop that I spoke with said w140s are very tightly sealed to prevent external noise from coming in. He told me that perhaps getting 2 12" subs in the trunk could do it. Does anybody have any recommendations on how to do this? I am not looking to have alot of bass. Just want to improve the system a little. My concern is that the bass won't get into the passenger compartment from the trunk - I don't want to blast the sub b/c I don't wanna wake up the neighbors either. Thanks so much.