Welcome to the forum . . . and greetings to Brooklin, Maine! I attended Wooden Boat School there in the early 90's, and camped in our old 25' AS right there on the water by the shop.
FYI there is a 20-footer thread, where you can get specific advice for our model:
https://www.airforums.com/forums/f54...rs-127845.html
There is also a Sticky Topic on winterizing in the Winterizing sub-forum, so for rough guidelines just go backwards in the process:
https://www.airforums.com/forums/f45...rize-7222.html
https://www.airforums.com/forums/f458/
Don't forget to flush out all the lines, incl. water heater, with good clean city water using an inline water filter, and new hose for potable water.
https://www.amazon.com/Camco-TastePU...xpY2s9dHJ1ZQ==
https://www.amazon.com/dp/B004RNOVTM...xpY2s9dHJ1ZQ==
You should also treat the water tank, pump, and water lines with a dilute bleach solution, and then flush them out well with city water:
https://www.google.com/search?q=wate...=airforums.com
Happy trails,
Peter
PS -- and the owner's manual, as just suggested.