Short trips are not relavant to the issue. Short trips cause internal corrosion, the discussion is external corrosion.
Ron
external corrosion is often a "too late" sign of heavy internal corrosion. I worked in the marine industry for almost 17 years; believe me, I've seen plenty of corrosion!
The Y pipe on my 99 GS400 just rusted through sending an O2 bad signal and tripped the check engine light. Welded up the hole and the code went away.
The pipe is made of a crap grade of stainless steel. Seem my 99 Chrysler exhaust is still shiny.