I like adirondack pond's idea of using 4" dia corrigated black pipe filled with expanding foam as a floation collar. The plastic fencing will work as a bottom mesh. Use the PVC pipe as inside framework to keep the shape and add a little floatation if ends are capped. A thin layer of peat moss should work as a planting medium. Once the plant roots are well established the root mass will unite the whole structure and should add floatation similar to a floating bog. http://www.youtube.com/watch?v=8PFIHgcPgNs http://www.paynesvillearea.com/news/headlinesarticles/archives/061803/0618bogs.html
