Step 2: Paddle bases
Next trace the sponges on the cardboard and cut out three for each sponge. It doesn't matter if you run out of graph paper, so long as you get one shape for each sponge. This will provide a guide for spacing the pins, without the hassle of measuring or marking.
Use hot glue to make cardboard-sponge-cardboard sandwiches.
Whee! We have reinvented foamboard. With graph paper on top.