Step 4: Adding the pockets
With luck, you'll have two shopping bags that are about the width of your cardboard when they are neatly folded. That's the size used by most convenience stores around here.
Start by placing the, flattened, bag over one of the cardboard covers, open end toward the center.
Tape down the bottom and two side edges of the bag. You'll notice that I placed a few maps in the bag I was working with to give it some mass and keep it from moving too much while i was doing this.
After the sides and bottom are taped down, put a pice of tape acros the top of the bag. This tape should line up with the the edge of the cardboard cover below it. You'v now, created a 10X10 plastic bag pocket (same size as you cardboard) on one side of your map case. Cover it with duct tape and repeat this process on the other cover.
When you finish, you'l have two, sloppy, plastic bag pockets with their open sides facing each other at the center.