Of course it is going to…
Of course it is going to rust, magnet or not. The bodies on these trucks are 302 stainless steel. Not a true stainless steel because it has carbon mixed in it when casted. They had to use 302 because it was easier to stamp the body panels. If they had used 304 instead, other problems would be present in the stamping process. 304 is alot stiffer and harder.