Trolley for Scadden Cast and Blast inflatable pontoon boat. The boat is very light but awkward to move by yourself. I couldn't find a good solution on-line but found the Makerpipe web page and gave it a try. I designed it 3 ways. I tried the 3/8 - 16 threaded inserts first and it worked better than I thought. Those things really bite into the pipe and hold firm. It would also work with a 1/2 threaded or plain rod through the pipe but this worked really well so didn't try the others.
https://www.davescaddenpaddlesports.com/product-page/dave-scadden-s-2023-cast-blast. I've attached pictures of the design and the source for the components.