I have been looking into HHO for about 2 months now. This in my opinion is the best cell design I've seen. It is a sealed cell, closed loop system. I can see adding a heater and pump to prevent freezing in winter. The end's of your plates and all electrical connections are external to the cell. And you can just add plates for different configurations. Here are a link to zero's you tube.
http://www.youtube.com/watch?v=_uEHF8wGNcs&feature=user