.I'm not sure how I would
safely use a gasoline can to fill the boat without a huge transfer
tube...

You buy the "jerry cans" not a regular boat tank. Then use a huge funnel. The
one I have has a 12" bell. Keep the can, funnel and gas filler touching at all
times during the filling process to avoid static. I can fill the boat without
spilling a drop. They also sell wheeled tanks that hold a lot of gas but that
depends on you having a clear path to the boat and a truck to haul the tank.
I did see a cool trailer at one of our JetSki rental operations. It had a 300
gallon tank and a self contained 12v pump with a regular fuel hose/nozzle like
they have at a gas station. The battery was solar charged. I wonder what DOT
would think about that? This one was operating in stealth mode (no hazmat
placards).