Materials: sturdy cardboard shipping box, utility knife, metal ruler, a pen or marker, strong tape such as clear duct tape.
Step 1: Sealing the back wall
First, tape down the flaps. Lay the long side flaps down first and tape them together at the seam in the middle. Then tape down the two shorter flaps, with a little bit of extra tape over the edges to keep them tight. I ordered them this way so that when you look inside the theater, the back wall is smooth and you could paint a backdrop right on the wall.