[wiredgeorge]

I don't think cold water left in a tank will eat an anode to the degree the one picture showed. I believe heat is the catalyst that causes the ion exchange that results in the rod getting eaten and not the tank. I would consider draining and doing some inspection of the tank using either a camera (not sure what they are called but mechanics use them for looking down spark plug wells and such) or a small mirror and flashlight. I have a small inspection mirror and flashlight and looked at my tank a bit as I have a very old camper and I wasn't confident of the tank.