I at least assumed you could get access to one
You can actually skip the bending and go to the hardware store and get some aluminum angle. They sell it at most hardware stores and it omes in varying half inch widths. You could get some 1/2" angle and cut it to length for all the corners and then you're just left with cutting rectangular pieces for the sides and top. No bending needed. Of course I'm assuming you can cut the angle to length. And also assuming you either have or can get acces to a drill for the holes.
Another idea would be to go find a plastic Rubbermaid container that's real close to the right size and cut and glue it to size. This only requires scissors but isn't gonna be very strong.