Sounds like cans is the way to go. But FWIW I was never planning to keep the caddy on the boat. I was looking at a 15 gallon caddy. Only time it would be in the boat is on the trip to and from the island. Upon arrival it would make to the dock, and I would use it to top off our two 6-gallon tanks as needed every morning.
I’ve spent some time plotting out routes to the various spots we are likely to fish. The good news is that our island is pretty centrally located. Some days we will put on 5 miles max, other days closer to 10. There is one trip I’m looking at that would be 14 miles round trip. I don’t think it will be necessary to go that far to find fish but I also like to explore and this area just looks cool.
When we’re using the outboard, it’s mostly going to be running on plane. Trolling will be done with the bow-mount and we’ll also spend a good chunk on spot-lock near islands and reefs.
Im going to do some testing next week to try to determine roughly how many hours/miles on plane I can get in one gallon. Should be interesting.