You are correct about the weight. I'm in the experimental stage now putting shelves in my new(er) van. I've pulled them out 3 times already because I keep trying to improve on them. I considered mounting a 3'x4' bolt bin for supplies but scratched it because of the weight factor.
If the guy thats going to do the lettering will get on the ball and get started, I can make the tool transfer from old raggley Dodge to new Dodge with payments and stop thinking about it.
I like the dbl luan idea. It will be slick though. May want to think about some rubber mats to keep tools from sliding around while driving.
I ended up making mine from 3/8 ply on 2x4 a frame.
Rubber mats were not in my budget, I put 3/4 x 3/4 divider strips every 10-12".
I also considered coating the shelves with some type of slip resistant...stuff.
Cool seal might work?