If you're not burning a lot of fuel, nothing beats the convenience of pulling up to the fuel dock and filling up. You don't have the pain - and hassle - of dragging gas cans down to the dock, bending over and lifting them to fill the boat. When I was living in Punta Gorda, FL, had the boat tied up to our dock in the back yard, I used a 21-gallon fuel caddy with wheels. To fill up the boat required 51-gallons, so it was multiple trips to the pump. Real PITA. I eventually stopped doing that and just paid the on-water prices for fuel. It was the cost of having fun.
We burn a lot of fuel (I typically go through about 30 gallons on a day trip), so the differential between dock prices and gas station prices was significant (we typically go out 2-3 times a week). When we moved back to Ft. Myers, we used to keep our boat in a wet slip at a marina. $178/month for the wet slip, and could not drag fuel to the boat if I wanted to (no fuel pumps at this marina either), so I still was paying on-water prices. I sat down and did some serious math and usage data, and decided that I was going to get a trailer and keep the boat in a 24/7 accessible storage facility.
So glad I did it.
I now trailer the boat to the gas station and fill up with non-ethanol at about $2.73 per gallon. That's a savings of over $30 each trip. My storage facility charges me $112/month, so saving about $60/month there as well. We also now take the boat everywhere - we're not limited to day trips out of Ft. Myers. We've trailered it down to The Keys 3 times already this year alone. I just pull up to the non-ethanol pump and fill both tanks up. (As a sidebar, I also take much better care of the boat now, as I can bring it home to clean it, I don't have to scrub the bottom weekly, don't have all the zinc maintenance, and do all my own maintenance now).