Here's an inflatable on craigslist:
http://washingtondc.craigslist.org/n...227708900.html

making boats:
http://yostwerks.com/

No duct tape involved unless you wanna... Somewhere there's this pretty hilarious link about a math graduate student who was building his own foldable boat and after building his frame, was super excited & wanted to try it out before getting the skin put on it - so he wrapped the frame with saran wrap & went off to the river to try the boat out.