Lux Box - Box Design

I am starting a portable storage company and I need to design the box a specific way. We need to make a design that we can send to a metal manufacturing company to pre-cast the materials needed for the box. It's actually a quite simple design once you understand what we are trying to accomplish.

We need a sturdy base, 4 corners that are able to stack 3 boxes high, and have replaceable side panels. I hope the pictures attached help