Opinion on your mixer valve. I've never ran one on my 55, but used one at home (wood heat). The mixer always seemed to have problems keeping the right temp. then not working at all. On my 55 the temp. stays fair enough, but if it gets too hot (shut off truck) and wait a minute before showering...
I look forward to seeing how you wire this all up, I'm taking notes! By the way, we've raised meat goats for twenty years and never took any camping. :) I'd rather hang with the goats than with most people.