My vote is for the Zodi stainless steel pump-up tank model. I have experimented with all kinds of variations as well.
2-3 good showers per tank, heats very quickly, no batteries to mess with, and the propane stove unit can double as your camp stove! I have had no issues with "O" rings yet. Nice unit which should give many years of service.
I will also vouch for the standing rack and rubber mat. I use a folding rack made of teak... works well and stores compactly. A rubber mat and cheap folding camp chair w/o arms works well too.
Happy showers!
