The old Mitsubishis rot for fun, mine only survived due to Ziebart and undersealing (everything... even the engine bay) by an owner that knew the importance of this. In the 3 or 4 years that I've owned it, I've never had to weld it beyond the original MOT repairs. I drive it daily and leave it out in the rain. Some areas aren't even undersealed properly now. I've always maintained that it's salt that kills cars so that's what I've avoided - I only drive it March to October. And this seems to work. Monthly inspections show it still to be as clean underneath as it was 20 years ago.
IMO the best solution is to do what I did - get two cars for two seasons. It's a good excuse to dip your toes in other brands and types of car.
IMO the best solution is to do what I did - get two cars for two seasons. It's a good excuse to dip your toes in other brands and types of car.