@ Just Jeff and Road Runners: the survey is a bit one sided yes, especially for the "why not?" questions. It kinda assumes people like to take showers for however long they want. I am really happy to see that this thread brings more quantitative answers (which I am actually looking for, except I needed some data on shower- usage time (which I actually should have related more to the amount of water in the boiler and fresh water tank) and on the amount of time it takes for water to heat with a boiler.
@ Just Jeff: It's not for just an A :) thanks for the interest! I actually really see myself living a free as in freedom lifestyle, so I have a personal interest in this project (which is a good motivation for me).
correction: I mean free as in freedom of traveling/ being on the move