Hey Guys,
I recently discovered a lightweight plastic modular toolbox that fits perfectly in a magliner jr with a shelf. Which is exactly what I was looking for. $100
http://www.keter.com/products/drawers-7-tool-chest
Pros:
2 of the 3 included sections fit under the backstage magliner shelf.
Locking
Sections are modular and they lock together
Lightweight, easy for me to disassemble and throw in the back of my car
Includes removable dividers and small parts containers
Cons:
Plastic, feels a little fisher-pricey.
Drawers latch hard and require some muscle to open, which can be an issue considering how light it is, so its not as smooth as a metal tool box.
Lightweight, needs to be strapped down to the cart to keep in place.
Haven't put it through a long field test, I update once it gets some miles on it.