We live in a cold climate here. Not unusual to hit -20 and have it stay there for a couple of weeks in Feb. Combine that with an average of 24" of snow on the ground and let's just say the brass monkeys are looking for parts.
Lots of good advise about draining pipes, using RV antifreeze (make sure you use the plumber or RV stuff cause the auto type is toxic) and removing all frezable items from inside. This includes toothpaste, shampoo, cans of soup etc. You really should remove all food anyway as you want to make the rig as unattractive to rodents as possible.
Change your engine and genny oil just before the storage, check all other fluid levels, make sure your rad antifreeze is good to -40. Lube all grease fittings. Clean the outside to spotless and put about 5 extra pounds of air in each tire. Fill your gas tank to the brim and add stabilizer. Run the engine and gennie to get stabilized fuel into the carb and injectors.
We cover and I suffer no damage from it. Keeps the ice from freezing to the roof and sides. I take my batteries out, charge them and store them in a cool dry location (my garage). Cold starts in real cold weather are hard on the engine so needless to say no exercising of engines but no ill effects.
I too park on planks to keep my tires up off the ground.
I normally winterize mid-October and it stays parked until late April. Short season but worth the effort.
2006 Damon Challenger 348F Ford V10
2013 Ford Taurus SEL AWD
Blue Ox Aventa & Brake Buddy