They seem to be doing very well here, we also get way to much salt on the roads, coupled with the dust that studded tires tear up from the roads, gravel and potholes etc. Plenty of I30's on the second hand market with 150000km-300000km that look good. I think that Hyundai do extra corrosion protection in Sweden though, on all newer models. They score well in all the tests the magazines make anyway. There seems to be some cubbyholes that might attract a little extra salt, like around the mudflaps that I make sure to rinse thoroughly when washing.
And as always, frequent washing in salty conditions, every two weeks they say here for a new car, more if you do a lot of kms, but once a month can't hurt even an older car. is always good for keeping rust off the car, especially if its in a climate that hovers both below and above freezing all winter like where I live. If its colder than -10 all winter its not as important, since the salt won't start to corrode until the water melts.
