Northern corrosion issues - aren't they fun?
Over here in southern Ontario, it's the same salt hill as Michigan and Ohio as we are just over the other side of the lake.
Now in western Canada, such as Saskatchewan and Alberta - they are super cold in the winter, but they don't use salt or other corrosive crap that eats vehicles. They use sand instead. So western vehicles are typically in far better shape.
I found out that as soon as the salt season ends and temperatures start to rise, you need to wash the vehicle undercarriage very thoroughly to remove every bit of salt residue. If you don't, the warmer temperatures will actually accelerate the rusting process if the salt residue is allowed to remain. So a good strategy would be to wash and dry the undercarriage, and then apply Rust Check or Krown or something like that. I used to use drain oil with a little diesel mixed in to make it penetrate better in an old paint spray gun, and spray bomb the underside of my former vehicle once or twice a year. It worked very well