Mine has never frozen, coldest it gets in there is the upper 30's though. My sister has been running a chest freezer in a uninsulated shed for 15 years, never had a problem, still runs fine.
Stick to the 5 shelf unit, the shelves are sturdier than the 3 shelf. Use mine for the car cleaning and detailing stuff, motorcycle helmets & boots, and the stereo. Works great for those kind of items.