Hi Henry,
My favourite winter fuel stabilizer for many years, has been Stabil.
Available in Walmarts, Canadian Tire, etc., it has provided me with fool-proof fuel storage solutions, on many boats, inboard and outboards, lawn mowers, snowblowers, gas weedeaters, etc.
How large in your fuel tank?
For my 100 US gallon tanks, I add a full bottle - 946 ml - of Stabil to each tank. 946 ml will treat a hundred gallons, but my tanks are not full, but it's ok to have extra Stabil in the fuel. Then, go for a few runs in the boat to mix it up and get fully through your engine. You will love the product and your engines will start up easily next spring. Here's a link to see the product I use.
Oh yes, it ALWAYS goes on sale in the fall, so look around. I can get the 946 ml size for around ten bucks, on sale.
Good luck.
http://www.canadiantire.ca/en/pdp/automotive/performance-chemicals/fuel-stabilizers-storage/regular-fuel-stabilizer/sta-bil-fuel-stabilizer-0380908p.html#.VCR6_rV0zIU