Drill with bits
Cheap baling or fence wire.
Step 1: Obtain Plexiglass
Step 2: Cut the Keyhole, Drill Airholes
Then drill 3 small (1/16" or so) airholes in each corner of each piece. That's 72 holes total. It's a lot of holes, but it is VERY important (prevents the watermelon from cooking in the sun, then rotting in the box).
Step 3: Assemble the Box
Step 4: Rotate the Melon As It Grows.
Step 5: Personalizing Your Melon
Another way to personalize the melon is to cut holes in the box to allow the watermelon to protrude. For example, you could cut a smiley face or anything that doesn't weaken the box too much. The watermelon won't grow into a design with details finer than about 1/2 inch. Also, If you use this personalization method, you'll have to dismantle the box to remove the watermelon.
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