Little Tykes made tugboat sandpits in the early 2000s. Little Tykes no longer makes them because people turned them into boats and drowned while playing with them.
How to Build a Tuggy Tugboat Sandbox Jetski
Step by Step Part 1
Tugboat Jetski part 2
Tugboat Jetski Part 3
Tugboat Jetski Part 4
Tugboat Jetski Part 5
Tugboat Jetski Part 6
Tugboat Jetski Part 7
Tugboat Jetski Part 8
Tugboat Jetski Part 9
Pool noodles are closed cell so they won’t fill with water.
Spray foam is open cell so they will.
I took roll on bed liner after the foam was evened out, and rolled it over to make a waterproof barrier.
I then took a piece of 1/2 plywood and screwed it in (with sealant to fill gaps) Caulked around the board to the plastic, and then did 4 coats of bed liner to the bottom of that and around 2 inches over the side, this made a waterproof, and abrasion resistant barrier.
The part where they failed, is they didn’t add posts to keep it straight in water. Use 2×3 boards along the bottom (I used 3, one centered and the other two about 4 inches in from the outside edge).