?? about a sub box and speaker combo

I found a sub box that fits in the spare tire well and it holds a single 12.I was lookin it up and the dimensions are : 11 1/16 mouting hole 24" diameter x 7.25" high.Now i want to put in a rockford HX2 and the specs on that are mounting depth of 5 13/16. I know the sub would fit, but it would be really close squeeze would i be better off just mounting it to a board over the tire well or would the sub have enough clearence in the box i mentioned?I am new to all this so i need any help i can get,thanks in advance.
 
y would u ever want a box taking up ur entire trunk!! im making a custom fiberglass enclosure that goes in the far back pass side and it goes to my spare tire hole and to my fenderwell and holds 2 10s, very nice, nevery light, and a much better space saver then a box.