I am making carrying trays for my son's 40K army. This is one of the four that will stack on top of each other.
I am using left over matte board. First I cut out the bottom piece. Then I figure out the inserts and draw a grid patter for where they fall. I then glue the sides on and then reenforce the sides with duct tape. I also cut out little grab rectangles on the side to make it easier to put the trays out. of the box they will go in.
Next step is cut out the dividers and glue them in. Last step is gluing a thin foam on the bottom and sides of the inserts.