I hunted in a floating blind at a place called Hood Lake Hunt Club.
Their blind would hold 5 or 6. It was about 6' deep by 18' long. Maybe 20'.
The base was larger on the front and back. I want to say it's 12' x 18-20'.
There was a 4' deck on the back so to speak. 2-footer on the front for dogs to sit on.
Under the base is billets of foam like a previous poster mentioned.
The blind is very stable and sturdy but never leaves the place it's at. Goes up and down with the water and is chained up to some cypress trees.
The blue barrel idea is no good. The reason. If only one barrel gets a hole or cracks...you are gunna be re-doing a lot of work or just dealing with the leaning duck-blind of Pizza.