Cavernous Crewmax DIY underseat storage

Very nice! This might be my next project.

 

After you remove the seats, and pull back the carpet, you'll find an 4-5 inch 'ledge' of metal just beneath the carpet at the extreme rear of the cab. This ledge slopes off as you move forward under the seats to an approximate depth of 2.5" as you reach the front location of the seat bolts. It's not uniformly flat across the bottom of the truck cab, so you have to make allowances for that as you cut the steam pans. Here's a view of the passengerside 'bay' showing the jack mount, before and after views. I also removed some of arm of the jack mount that protrudes vertically and inconveniently, and rotated the jack 180 degrees so that the crank assembly is no longer facing forward into the storage area.

 

Took the tape measure out to the truck and did some measuring....
There is a stout metal tube running horizontally beneath the seats. From the bottom of that bar to the bottom of the "pans" measures 5 1/4".
The drivers-side and the passenger-side pans are approximately 11 inches wide. The center pan is 15" wide. It's made up of 2 pans cut down the middle, overlapped, and bonded together using JB Weld. (Amazing Stuff, that JB Weld!)
The Passenger-side pan is roughly 7 1/2" from front to the jack mount. The drivers side and center pans are roughly 12" front to back but with additional length "up the rear slope" previously mentioned.

Got quite a bit of practice using the angle grinder. The jigsaw came in handy as well, as did a file, square, razor knife, can of spray-on bedliner, and permanent marker. Even used an old crayon to mark the carpet. I also had to do some modification to the middle seatbelt attachment point, but I can cover that at a later time, should someone request the info.