Cool diary, a nice read.
I think you're overestimating the risk of hydrogen explosion. It is only flammable in concentrations of more than 4%. If you don't cover the electrolyzer with anything I'm pretty certain the minute quantities of hydrogen produced will mix with the air. If there's even minimal ventilation hidrogen will never have a chance to reach a dangerous concentration.
Apparently running 10 Amps for an hour produces 0.38 grams, or 4 litres of hydrogen:
http://www.wolframalpha.com/input/?i...%27s+number%29
http://www.wolframalpha.com/input/?i=0.186+mol+of+H2
The energy density of H2 as fuel is 3 times that of petrol.