I wonder how it's possible to get an effective hull shape using a folded sheet.

ahh, you folks need more Google-Fu!

Here the patent and drawings:
http://www.google.com/patents/US20110017121

its made of Coroplast, a corrugated plastic sheet. Scored, not cut...think papercraft. Very tough, bike folks have been making velomobile shells out of it for decades. Probably develop small cracks over time, but should be obvious and gaffer tape-able, for the short term. I'd be much more concerned about the lack of float bags, or any offer to sell em with it....