I do it this way
I winterize the plumbing (potable water, head, shower sump, AC) while the boat is in the water because it's easier to get the antifreeze on board from the dock than lugging it up a ladder. Also, I'm not climbing up and down with dirty shoes from the parking lot. I put the engine antifreeze on board while the boat is in the water for use later for the same reason.While still in the water, I change oil and fuel filters because it's easier to run the engine to warm the oil while the boat is in the water.Once the boat is hauled, I run the engine to pump a few gallons of fresh water through the cooling system. Then I stick the raw water pickup hose into a bucket of engine antifreeze and keep running the engine until the antifreeze comes out the exhaust.Done!