just make a custom box there are tons of write-ups all over the web and find yourself a nice pair of subs or 1 idk how much boom you want and take it from there. As most "box" sets that places like quadratec sells are quite expensive and would make a very nice footrest because they are selling to people who dont have the most knowledge on things of this matter. Just do some research on boxes that will fit in ur LJ, and proper amp and subwoofers for what you want. It should take less than a couple hours to find everything you need and you will be much much happier