were you by chance fixing a leak where the two body panels met right behind the woofer box? I've been battling the same thing and just fixed it myself. How did you fix your problem there?
Since I am in a similar situation, I also lost a bolt, but only one, to the subwoofer box. I haven't had need to replace it yet but I will be doing so soon and if you still haven't found the thread size by then I will communicate the info to ya