I ordered some sub boxes from a place in cali they come in a set of 2 and they come with very specific dimensions so I made sure the subs I wanted would be a good match before I ordered them (Sony Xplod 10") I have always had good luck with them and have yet to blow them regardless of my Planet Audio 1200W Class D amp cranked up. I got the boxes and had to remove the back of the seats so I could trace around them on the back panel. Remove back panel cut out the placement for the boxes. Now I had to remove the cab vents that are fitted into the rear wall of the cab and I cut out some plexi glass to cover those but before mounting with rivets I placed a bead of butyl tape (window weld) around the edge to make it water proof, then cover the edges of the plexi with a waterproofing duct tape (sold at walmart) just for good measure and to cover any sharp edges and then drilled and riveted into place with 1/8 rivets.
Had to remove the jack holder from behind/under the rear pass side seat. To do so, I used a 3/8 drill bit to drill out the 6 spot welds (just small circles on the plate surface). After that I went to my local tractor supply store and got some "Christmas tree" fender holders and found some with 3/8 diameter and placed some waterproofing tape over the holes and pushed the Christmas trees through the holes.
Now took apart the back of the seats and just dealt with the metal framing of the seat. I knew that the subs would hit the bottom framing tube of the seat backs so I cut out the tubing at the bottom of the seat frame and partially the support rods coming from the top of the seat to the bottom and I cut some metal rod and welded it in place so that the support rods weren't just sitting there poking through the back of the seats and if for some reason someone was in the back seat and I got in an accident there is less of a chance of having those support rods going through someones body (just good measure once again). And now I am waiting for my subs to come in at walmart since the older version of 10" xplod are $30 and there is no mechanical/technical difference.