Floating rail in the Delta

I'm thinking about building a small flat box that floats and using it in the delta but I need some advice.

First off does anyone know what the laws are on this? If we are hitting it and the sheriff pulls up is it illegal? I'm sure it depends on the sheriff but I'm just curious on what the actual law states.

Next, I've never built a rail or box before but I'm thinking of just using 2-3 plastic 55 gallon barrels to float the rail and to build it in sections to make transporting it out there easier. Will the barrels work or does anyone have any other advice to make it easier or work better? Also what is the plastic called that all the rails at the cable parks are built out of and where can I get some?

Thanks in advance!!