I drove over to have some work done on a rifle yesterday. A new gunsmith to me but one I hear good things about, a British shotgun maker trained gunsmith. While I was there he pulled out a DHE #1 frame, 16 ga. that someone had dropped off at the shop. He had the stock off and the frame and barrels on a table.
The bores were mirror, mint condition and the stock was well used but well cared for.
but , the gun was trash!

The outside of the barrels were rusted and had pits that looked to be a 32nd or more in depth. The frame was rusted to the point that no engraving was visible. He said that he had to hammer the barrels open because they were rusted so bad. He was parting it out; stock, skeleton butt, ... etc.
I asked how this happened, suggesting it looked like it was a boat gun kept at sea. He said the customer that dropped it off told him it was his mothers and she used it regularly but when she died they put it away for 7 or 8 years without looking at it. When the did, it was in the condition I described.
It was stored in a leather gun slip that was lined with lambs wool and by sitting in it for a long period had ruined the Parker. I had been told since I was a kid, never to store a gun in an air tight gun case or in a wool lined gun slip because it will rust the gun; this is the first time I have seen the results firsthand.