Parametric Sliding Storage Box

I'm frequently in need of a simple storage box and I don't want it to have anything extra in the way of hinges or snaps. This box slides together and there is a simple strip in the middle that keeps in closed.

I've included the Fusion 360 design file. In Fusion 360 if you go into “Modify -→ Change Parameters” you can change the parameters width, length, and height.

I'm not sure how to make the pattern use a formulae (aka use parameters), but if someone knows how, please let me know.

If you print the outer box standing up on end and the inner box flat on it's bottom, you don't need any supports.

Please let me know if you feel there are ways to improve the design.