I put it in for summer storage. Just follow the directions on the can. 1 oz. per gallon. My sleds have always started right up in the fall without any carb cleaning. Use non ethanol gas if you can along with the Seafoam. I do not put it in during the riding season. Gas never stays long enough in the tank to need it!
I do the same. Non-ethanol gas, 1oz per gallon. I make it habit to start them once a month in non-sledding months. Buy a rear-bar lifter ($55) to raise the track so you can pull on the throttle for those off-season starts
I use a product called k100 which you add directly to your tank. It works well for keeping everyone clean. I have a carbed vector (2006) which was sputtering when it idled, because she sat all the time. The previous owner put 500 miles on in the past 6 years! I ran some k100 through and the sputtering toned itself down quite a bit. Seafood just didn't do as good of a job I noticed.