The fiberglass tanks look like they would be perfect for the dink with the propane outboard, but at those prices I wonder if they would be theft magnets? I see lots of pretty rusty looking tanks in those tank exchange cages, but I really don't know much about how they work. I've always owned my own tanks that I got refilled. You can drastically cut down on the rusting of a standard propane tank by painting it with bettern stuff--I used to use yellow zinc chromate paint which had the added advantage that I could spot my cylinders from a mile away and they never got mixed up with anyone elses. But, as you say when you are out cruising it won't be easy to get propane some places.