I have access to unprocessed double wall corrugated box material, I have fabricated a custom box with two layers of double wall with a layer in-between with the flutes going the other direction, this will add strength & resistance to bending. There is a shape drawn on both sides of the box of the strips. You have to use a razor knife with a new blade to open, just cut around the drawing. You might think it will be easier to split the layers, it will not, everything is laminated together with very sticky industrial two way tape.