Being from the Northwest, I can't comment from direct experience since they sand roads here and temps don't drop as low as they will for you, but I can regurgitate what I've heard from others in more harsh climates.

Besides getting a good application (or three) of wax on the painted surfaces, wash as often as possible - at least a good rinsing once a week (wheel-wells, body drains, especially). Also, I've heard not to park in a heated garage, as that will accelerate rust growth. Covered, and garage parking is fine, just no heat.

Regards,
- Ryan

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'95 E420 - 'Shadowfax' 138kmi.
'92 Volvo 740Turbo Bard 193kmi
'74 240D - 'Ol' Green' 4spd Manual 104kmi. (sold )
'77 300D - 'Red' 223kmi (sold)
'75 240D - 'Bianca the Blue Bomber' (sold)