Well I got tired of having the whole xtra cab and only having the little wimpy shelf that wouldn't hold anything and always came loose so I made a little storage box in the same place. Its the same dimensions and it opens up a whole lot more space for tools, straps or anything else you want back there.
You gotta have a little bit of woodworking competency in order to get the profile of the transmission hump and the pointless hump in the rear wall of the cab but if you can hold a board in place and draw with a pencil on a stick your fine.
To get the front face board in place you have to make a little bracket out of some steel strap that will bend over the original shelf brackets so you can bolt the face board onto it.
the bracket is circled in red.

For the top door you have to profile the rear of the cab onto a board and cut out the shape then cut that off of the whole door piece so you can get a piano hinge or something in there. This lets it fold up without binding on the rear wall hump. I screwed the piano hinge onto the door and the profile strip and then ran a carriage bolt through the strip and into the far hole on the seat bracket, and anouther small screw into it from a little bracket in the middle.

I think it works great. You could also mount speakers in the front face if you got em.

 

thats really cool, did you use plywood?

 

The front is some cheap ass ply we had laying around from work and the top is a piece of nicer doug fir. Wish I had something nicer for the front but whatever. Been looking around and hadn't seen anybody else with this so I thought I'd share.