If you're referring to rust other than exhaust, it's really hard to avoid.
Like you I winter store my Z ( live in Mich. ). In the fall before storage I put it up on the lift and toatally wipe down the under carriage. There are suspension parts that get the finish chipped off from loose gravel and sand blasted from every day driving, even when you only drive it 4/5000 mi.a year! Winter thru spring any big temp. swings the car sweats and the vulnerable parts begin to corrode, yeah it sucks, but we are doing all we can do to keep it to a minimum! It would really look like sh*t if we drove our cars all winter!
Don't mind me I'm just rattling on .......
