IIRC, My box was as big as I could fit behind the seats, and it was 7.5" at the bottom and it tapered to 3" at the top. It was 13" tall and 36" wide. 13" is as tall as you can go becasue there is rib on the back of the cab.
I had box that was taller, but it was open in the back above the rib for some 6x9's. I also swapped in the trim panels from a Gen II Ranger w/o speaker pods so I could make the box wider
These were the 12" JL's I ran with my Memphis amp. There are also 2- 6x9's, 2- 4x6's and 2- 3x5's. It was the source for music at all of our parties/bonfires.lol When I built this box I had no idea that air space was so critical for a sub to sound right.
Here is my Memphis S-Class subs in the old reg cab before I put them in the blue truck. (that is my inverter, not my amp.lol The amp is 3X that size.) Notice rear panels with speaker pods vs the pods w/o in the pic above. This box was built to have the perfect air space for a sealed box with two subs. I made it out of 3/4 MDF and sealed it and wrapped it in black leather. Haveing the correct size box makes these 10's way deeper and more precise than my old setup.
Here is the same box in my Super Cab. I had to trim a little off the rear interior panel and lose the cargo cover/shade thing as well as the net on the back wall, but it was worth it. The biggest down fall is I have to take out the box if I want to fold down the jump seats, but it gives me an excuse to not have to haul more than one extra person around. Put the quick disconnect terminals on the box so it only takes a min to unplug the box and throw it in the bed or leave it at house if I need more passenger room.
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-PlumCrazy