Do the subwoofers only come on the el's? I want to buy one and put it in the same panel on my 07 but I don't think I have the space. Can anyone tell me if they've added an aftermarket one and where they put it. I usually have lots of stuff in the trunk for work and don't have the space to put a large subwoofer back there. I'll take any ideas as to how you'd put one in too, I have a few ideas for this but want to hear if anyone might have a better one.