I built a similar one and floated it with those pool noodles like Catmandoo, but had a couple problems.
First, the noodles floated it so the top was just a couple inches above the water and though it worked well for holding my HBG and BG, the catfish would go over the top every time. I lost several, including my daughter's 5 lb pond record - not very happy with Daddy the next morning. I like the way you have it, Tbar, suspended up outa the water a bit.
Second problem is that by the end of the first summer, the noodles had been exposed to the sun too long and began shedding little pieces that would get all over your hands and could be seen floating in the water.
Thanks for posting those pictures, I hadn't thought of hanging it off the side of the dock.