I built this last year after much inspiration from this site. The platform has two full length drawers sliding on Delrin strips. There are two top hatches for each drawer for access when the back is shut.
I found the sleeping pads/chairs took up too much drawer space so I made the overhead storage using steel tubing with shock cord run through. The mounting holes use the holes already there from the bolt on rack gutters. Works great, can't see it at all out the rear view mirror and is forward enough to be well out of heads reach when sitting on the platform. I can also store two bikes upright with the front wheels taken off, so all loaded it's a pretty incognito setup, minimal wind drag, bike stay protected, etc..
I also have a Kirkhams auto canopy with brackets that I made to use the two side rack bolt on gutter mounts.
It's worked great for us with one kid. We rode out a couple nasty dust/wind storms around Moab and it was nice. I gotta admit though my mind is kicking around a custom hard shell pop up... standing up would slick.