I run marine stabil ethanol treatment (it is not the same as red stabil). I also put in some ring free (or you could use seafoam) in every fill up no matter what time of year. Winter is also a good time to get yearly maintenance done (lower unit oil, pack bearings, check lights, plugs, batteries....). If you are going to store it outside be sure to drain all the water out it by lowering your motor all the way down.

I use mine most of the year, so winterizing for me is putting in some extra clothes, coats, hats and gloves.