Re: winterizing
The reason for antifreeze is to keep water from freezing. This is not because there is anything wrong with ice, but because water expands when it freezes, and if it is contained during the freezing process, the container is usually damaged.
If the tanks are really empty, why would you add any antifreeze? Any trace of liquid remaining would have plenty of room to expand, so no damage is likely.
Then there is the fresh water tank and the heater tank. Did you drain them? Generally these don't drain all the way, but again, there should be plenty of room for the water to expand when it freezes, so is not critical, and cleaning the antifreeze out of these tanks is a challange.
The place where antifreeze is critical is in the lines, where any trapped water will expand and can split the lines. The right amount is the amount it takes to fill all the lines (comes out at every tap or other water source).