Rust INSIDE a shed

Lack of ventilation and condensation. Is there a moisture barrier atop the ground the shed sits on? That plywood is of little help and may be rotting on the underside. Given the right atmospheric conditions, the warm moist air can condense and coat everything inside. I once saw my tablesaw top rust before my eyes as it was cold and a warm moist breeze came in when I opened the door.

Agree: Probably condensation. We added a door ventilator to one of our sheds to try and keep the temp. inside closer to outside. Although shed, built of scrap wood was pretty leaky anyway. Also; where is moisture coming from? Changes of tempeartire during humid weather or when raining? Damp floor? What is often called 'Rising Damp' due to lack of vapour barrier between floor and ground? That's one reason have always built our sheds/cabins above ground on posts to allow air space below

Could be something like this: I have a large metal roof carport with open sides. Fog, dew, or frost collects on all surfaces top and bottom. When the sun comes up and melts the frost, it rains inside my carport almost every day in the winter. I'm in So. OR.

Kevin