We attached both the long and short sides to the legs, instead of each other. We uses 2" screws to attach the short side and 1 1/4" screes for the long sides. Make sure to pre-drill your holes. These boards can easily split, weakening the structure.
We used the last 3 shorter boards as supports for the plastic container by attaching them with 2" screws to the underside of the longer boards. I used a Sterilite 41 quart under bed container.
I purchased a few cheap water toys from Target and it was ready for playing!
Thanks Dad for helping me with this project!