This will be my first winter as a boat owner. Do I really need to "winterize" my I/O motor{Mercruiser 120) if it will be stored in a basement garage in Central Alabama?

BamaJoe, it's always a good idea to fully charge all boat batteries for storage and add gasoline treatment to any gas left in the tank.
My question, why quit boating in Alabama so soon?
If you do put it away, remove the prop look for line, wire or anything around the prop hub, check the hub spline to see if it's bent etc. If possible raise the trailer tires off the cement, keeps them from developing flast spots during the winter. Not much else needs done, maybe drain all live wells, bilge area and warter rfrom around prop hub. So do the trick. Johnnie

Joe, Johnnie pretty much covered it. I'd like to add that at the end of the season, and up here for cold weather purposes(tends to be a tad colder here than there about december) I drain and refill my lower unit oil. This ensures that if there was a seal leak and water entered, it will be drained. And if water is present, this is a good time to replace seals, since it won't be interfering with valuable fishing time. Also, any metal particles from normal wear will be drained allowing the new oil to do it's job better.