I've received some questions on my build via PM so I thought I'd answer what I could here. I built mine myself, and I don't have any plans. I just kind of designed it as I built it. But it was pretty simple. The frame portion is made of 1" by 4"s. I just measured the length from the where the flat part of the back transitions to that slope to the back seats all the way to about 1 or 2" from the edge of the carpet. You can see in these two pics.
For the width you can see its pretty much right up against the wheel wheels on either side. Maybe 1/2" on either side or so.
Now, I was anxious to get going and got my drawer sliders from Home Depot. Consequently, the longest I could get there were 22". So that is why I have that dead space at the back. If I did it again I'd probably get longer drawer sliders and make deeper drawers. I can still use that dead space but it will be inaccessible with the back loaded. Anywho, that's why my drawers only go that deep. I then just found the middle and put another 1 by 4" lengthwise to make the divider between the two drawers. Then I made sure the middle piece was square and put a narrow strip maybe 1/2" thick or so across the top in the back. THis is really just to provide some stability to the shape (to make the drawers slide easily) and to provide a place to mount the latch catches. The drawer boxes were made with 1"x3"s. Again, I just measured off the frame I just built and cut to the proper width and depth. No fancy calculations. Installed the drawer bottoms and sliders and was on my way. For the platform that goes on top, I didn't end up affixing it to the top of the drawer box in any way. It is just sitting on top. Its heavy enough that its not going anywhere and I can just lift it up and access that dead space area I talked about when the back is empty.
Finally, you can see from this pic how much additional height there is between the top of the platform and the seat back when folded flat:
Now, this is a bit higher than it needs to be because I opted to use a pretty thick carpet pad on my platform to make it extra comfortable. But you can see I had about 2 1/2" to raise up the seat back. Its a bit less than that towards the front as you probably know the seats aren't perfectly flat. So I made these smaller platforms to go over each seat back. I used the same carpet pad and carpet so it is pretty seamless. As I said the seat back is not totally flat (a bit higher towards the front of the truck) so I put some risers on the bottom of the seat back pad that are a little taller under the back section. Hopefully you see what I am talking about in this pic of the bottom side of the seat back platform:
The final result looks like this:
So it's pretty modular in that I can keep the drawers and platform in there all the time (with the seats in their functional position) and only lose a few inches of head room in the back. Then I can fold either or both seats down and have a flat platform if I through in one or both of my seat back panels. FInally, as I mentioned in the earlier thread I built little platforms with legs so I can take the seat bottoms completely out and have over 6 feet of sleeping room back there if I want. Hope this is informative!
Doug