Before I start I would like to preface that I know I could blow up using propane on the boat. Now, I would like to build an enclosure on my roof that would hold two 20# bottles and on the outside mount a 5gal/min on demand water heater. It will be on the roof that if the gas leaks it will go over the side. I would pipe down to the galley on the outside and stub into a stove. Maybe pipe down to the aft for a grill. The hot water would go down the wall and be distributed to a shower and sinks. Does anyone have any experience with doing this or experience at a dirt house on how much fuel will be used? Thanks Paul