Originally Posted by Breadbug
After removing the interior I can see a spot of corrosion on the inside of the exterior skin. What can I do to stabilize it? Paint? I seems to be the air conditioner that might have caused this. It is right next to the roof support by the air conditioner.
From what I can tell from the pic it appears to be rusty in color. If that is the case you may have to carefully inspect the AC. Corroding parts in AC can track the molecules of steel carried by moisture along your skins. In any event the moisture appears to be the culprit. Remove loose stuff with sandpaper. Wearing face shield protective clothing and gloves spray affected area with Aluminex By Marykate. This oxidation remover should be available in your local boat stores. While wet wire brush the affected area with Stainless Steel [only] brush until clean. Wipe down several times with soaked in warm water rag. Neutralize the surfaces with Alondine design for aluminum surface prep. Paint with suitable aluminum primer. What is important that you eliminate rusty parts in AC and stop the leakage. Thanks, "boatdoc"