Well, being up North, you already know to hose down the undercarriage of a vehicle/boat/camper during the winter due to the salt. Don't want to rust out your frame and fasteners or acid etch your aluminum siding.
I second the advice to get tire covers. And if you don't want to jack up the axle itself, just put down any and all stabilizer jacks. Best two things you can do to prolong your camper's tire life, to my knowledge.
Wrap your trailer wiring in split loom to prevent corrosion.
Most sealants degrade with exposure to ultraviolet light. I'd be more concerned with that than freeze/thaw cycles. So I like the carport idea.
So long as you have plenty of grease in your hubs, the bearings won't rust.
I know it's not much information, but I hope it helps