Winter lay-up, in the order that matters
Lay-up is a sequence and the order is what makes it work. Every water system drains first, including the ones you forgot exist, because a frozen calorifier splits and you will not know until spring. Fuel tanks go full, not empty, so there is no headspace for condensation to form in. Batteries come off the boat entirely and live somewhere they can be trickle-charged, since a flat lead-acid battery left through a cold snap is a dead lead-acid battery. Covers go on last, ventilated, or you have simply built a damp cupboard.