Even that won't do it. You'll need 4 of em, MAYBE then you can rattle the windows on some buildings, OR a couple 15s.
Also you need to keep in mind ratings for your subs. Look up what Alpine recommends giving them for size, factor in port size and box thickness, etc etc. You should be able to give them plenty of space with plenty of room. You should also be able to build it outside the trunk and then drop it in. But if you go too big for your subs you could ruin them, so as I said, go by what your manufacturer recommends.
