My friend Matt Riley did that float about 20 years ago with a bunch of punks. It used to be a thing, not sure if it still happens or not but it can certainly be done. He was on some plywood shit they built on 55 gallon plastic drums. He said it was pretty rad, a lot of folks that live on the river would invite them onto their property for feasts, or to camp. You can find a few stories written up online searching "punks float Mississippi".