Dammit you're building what has been floating around in my head for months now.
For the chuck box check out the designs that Drifta has for his kitchens. I find most designs are pretty skimp on actual work space when you fold it out, Drifta seems to have prioritized designs that fold out into lots of work space.
Also for the interior dinette the table should be able to double as an outside table, cut down on one more item to pack along.
Lastly is the interior, the euro guys do a good job keeping weight down using flight case components to build out the interior. You can see good examples and the components here.
http://www.4x4-innenausbau.de/ I think this would also keep the cost down vs lots of custom metal or composite work.
The other design that I've been thinking about is a flat deck design where the back wall still has the ability to drop a tail gate so you can carry sheets of 4x8 ply or lumber in it. I've got limited space and don't have the room to store a pop up shell off the truck as I don't want to tie up my whole garage, and still need to use the truck as a truck. This idea is more like a contractors bed/cap but the top pops up for weekend camping.