Cut off the excess and cut a slit down each corner on one side. Then cut around the top of the deck to have one flat part(flap). Cut strips of magnet for the clasp. Then put tape under the flap then put a magnet in black side up. Then fold the excess over. Thin the sides by trimming excess.
Step 6: The cold clasp of death
Put the magnetic faces together, and fold over to find out the mounting location of the magnet. To secure the magnet put a piece of tape over it.
Step 7: Additional Ideas
Put rolled up piece of tape over the magnet.
Tuck the flap in.