If I was storing in a heated storage, I would blow out all the water lines, make sure all tanks were completely empty, uncluding the water heater.
WHY?? Just in case for some reason the heating unit would breakdown or loose heat for some reason.
But I would also pump anti-freeze in the water lines and dump a cup or so down the drains.
Remove the batteries and put them on a Battery Tender for the winter.
Increase the air pressure in tires to their max limit on the sidewalls for storage. Place Bounce Fabric sheets around inside and also in the storage compartments. Makes a nice smelling RV and according to some helps keep the rodents out, they don't like the smell.
In other words, If it was mine, I would winterize it just like I would when storing outside in the cold. But that is me!
Ron