I think Tom's idea is the best one here in the USA--use the exchange cylinders and you'll get a fresh one every once in awhile, so rust isn't such a big issue. For longer range cruising there is the problem that it is rare to find propane at a fuel dock or even close to one. Having aluminum tanks would reduce the weight somewhat, but you would still be humping them around trying to find propane, and it is true that they are frowned upon in buses. I have found a lot of cab drivers will take them no problem though. You would get rid of the phase separation issue that you get with ethanol gas, and no worries about water getting into the gas tank when the dinghy is swamped in a rain storm. Seems like it might be very viable for USA cruising.