I would personally not want any kind of propane on my boat. get a leak and it sinks to the bilge and when you run the bilge pump.. boom. But its your call, wait for someone with the right info to see this.
Propane is much cheeper here, runs cleaner, less risk of spillage, tanks take up less space, produces less carbon for longer engine life, used extensively in cars and trucks.
Have you heard of any kits to adapt propane to outboard engines?????