What you will need:
Rubber tubing (1/4 latex hose. You should probably use 3 ft. I used 2 ft and it wasn't enough. I found some in the plumbing aisle at Lowe's)
Glue (Anything that will bond wood and rubber, I used Gorilla Glue)
Binder (normal 3-ring binder)
Step 1: cutting the wood
Cut 4 pieces like these. Approx 1 1/2" x 1 1/2" L-shaped pieces.