Yes it will start rusting with any moisture. We can see that on our disc brakes. But I'm not understanding what the point is here. If you have a nice solid outwardly appearing rust free truck that is kept dry 99% of the time as my '79 is, what should I do? It has survived for over 40 years without this supposed hidden rust extending to the outer panels but is the implication here that I need to start drilling out rivets and removing skins to treat the inner panels?