Hi, Montreal winters here Mass is a bit milder, and probably a bit more problematic that deep winter. Salt in the cold is not great, but salt and freeze-thaw cycles are really hard on cars.
I would store it if you want it to survive. But, given that it's already rusted, maybe get another mint car for the summer, and enjoy this one as long as you can.

If you do choose to drive it:

• fresh undercoating (the oily kind that spreads). See if you can get a spray bottle to take home to reapply to wheel arches through the season.
• Pack wheel arches with bearing grease, tar or something similar (when they're dry so you're not sealing moisture in). That's the weakest point, especially the little step forward of the rear wheel wells. It's like it's made to collect snow and water.
• minimize exposure to liquid water. If you park indoors, find a way to not, or at least in a well ventilated, cool dry space. If you can't not park indoors, wash it as often as you can so its not sitting warm and salty.
• If you park outdoors park on well-drained asphalt or concrete so you're not accumulating humidity under the car
• fix the rust before it spreads. Use POR14 or some other strong metal treatment
• winter tires
• make sure your battery is in good shape
• clean grounding points, the electrical system mitigates oxidation of metal parts to an extent

My 2004 has maybe 10 winters driven and 6 winters stored/minimally driven. The rear wells needed attention a few years back, but all things considered, undercoating and proper salt management works. No perforation anywhere.

 

Thank you for the tips, any recommendations on tires? I've got 225/40s and 18s.