I'm assuming when you say island you're talking about a tiny,tiny island on a lake. I mean what kind of a Banana would fill his water jugs at a shoreline unless it was a lake? Nobody in their right mind would grow with salt water!
So if you want help & ideas brah, you're gonna have to be a little more open about your location etc.,etc..
I suggest that perhaps you should grow closer to your home base. You sound like you're not gonna be able to check your patch often. Don't expect miracles if you can only tend to them once a week, or so.
Bottomline , you're gonna have to pack in some good soil. Pick your spot, and go dig your holes one week or two before you plant.