Re: Should I add Sta-bil?
I would go with a slight variation/combination of some of the above posts.
First, Sta-bil is brand and they really have 3 types you could choose from:
1-marine
2-ethonol
3-fuel stabilizer
I have not looked at the labels/content-make-up to know exactly how they might differ so I would first vote to use the Marine blend.
I would add 2 ounces now as I also believe "it couldn't hurt" but I would also had 2 gallons of premium to mix with it. If the boat is on a trailer and it can be moved, after adding the fuel, drive it around in an attempt to "mix it in".
Then before the first start in April, add another 1 ounce of Sta-bil along with another 5 gallons of premium.
Run it on a hose/muffs if at all possible first and make sure it seems to run normal.
Use the boat enough where you think you've burned around 15 gallons, then change the fuel filter.
As a side note, my Sea Ray has a 100 gallon tank which I never try and fill more than 3/4 but I also add the Merc stabilizer product every time I add gas and not had an issue in the 2 1/2 years we've owned it and just like you, I've probably got around 20 gallons of gas in there for more months than you and will do similar to what I described when we start using it again. Only difference might be is that when the boat is not being used, I still run it on a hose about every 3 weeks.
Mark