Skip ahead a couple of steps, and you can see progress:



Then I stretched fleece fabric across the gap, and used a hot glue gun to attach everything (used it for the dowel legs also):



Then more resin. This stuff could knock out a cow. It is so nasty smelling you'll want to puke--I still have some resin smell in the Xterra.



I decided the bottom could benefit from a fourth layer of mat to make it even stronger:



Then you've got to cut off any jagged edges, and sand it smooth. I decided not to smooth out this box with bondo simply because it was going to be 90% hidden, and covered with carpet besides.



Then, the box was carpeted and the sub was installed. I drilled a couple small holes for speaker wire going into the box and then hot glued the holes to ensure no air leaks. I also put down one layer of Ensolite inside the box to keep the wires from buzzing against the fiberglass inside.



Finally, the sub can move in to it's new home: