The only problem with that canoe is that if you drop your knife you're going down like the Titanic <img src="/ubbthreads/images/graemlins/doh.gif" alt="" />. I don't think that 4mil plastic is going to stop a nicely sharpened Scrap Yard blade!
On second thought, I guess if he sealed off the ends of the PVC pipes to where they were air tight, you wouldn't go to the bottom, but you would definitely still get wet.... <img src="/ubbthreads/images/graemlins/laugh.gif" alt="" />