Here is what I recommend. When you are finished with the boat at the end of the season shut off the fuel to the carburetor. Run the engine around 1500rpm's until it sucks all the fuel out of the carburetor. This insures it will not have fuel drying up in it and leaving behind any residue or "varnish".
As for the fuel in the tank I run Marine or "rec gas" for the first and last tanks of the season. All season long I just use plain old 87 octane pump gas. Zero issues for decades now with the boats I've owned doing this.
I'll add here that the same thing applies to small power equipment, chainsaws, string trimmers, leaf blowers, small standby generators, etc. When you are done with them for the season get them running, dump or drain out all the fuel, then shut off the fuel to the carb and run them until they stall out. If possible pull the choke just as they stall to suck all the fuel out of the carburetor.
I have ZERO issues with any of my power equipment here and have been doing this for at least 25 years now. I don't avoid fuel with ethanol in it, I just make sure it doesn't stay in the tank very long and never in the carb for long periods of time.
I'd also mention here that additives like Stabil and Sea Foam, etc, do NOT protect you from fuel going bad, water absorbing water or clogging up you carburetor. I work on small power equipment and have for over 40 years now and see ALL the aftermath of folks relying on these products to protect them from bad fuel, which they do not........FWIW......