I get asked everyday about frame rust. Usually everyone thinks that because we are in the northern U.S., every corvette has a rusty frame. What most people do not realize is that we buy corvettes from all over the country, and even the ones we buy in the north often come from other parts of the country prior to coming here. Same goes for corvettes for sale in the south- many have spent time in the northern states before ending up where they are.
The most common cause of rust, I have found, is not road salt- the two biggest causes are mud and mice. GM designed the corvette frames so water and dirt can pass through the inside and exit out the factory holes. The problem is, if you do not take the time to clean the mud out of the frame occasionally, it plugs the holes and eats the frame from the inside out. The other major issue is mice- they take all the carpet padding and what ever is laying around the garage and build a really nice home inside the frame. So now you have not only a blockage issue, but also additional moisture with high acid content eating through the frame.
North or south, I check the frame of every car I buy. If the frame is rusted out, I don’t buy it (unless we’re talking about a parts car). Every corvette I buy gets the frame hosed out to clear any blockages, so that it stands a chance of living another 40 years.