A guy at the Glen Ellyn show said my cover was trapping moisture, and he was right
I had my 68 cutlass under a plain tarp in the driveway for 2 winters, and he told me flat out that I was basically steaming the roof and trunk. Pulled the cover back and there was condensation on the trunk lid and a little surface rust starting near the rear window. Switched to a breathable cover on a frame that lets air move underneath, and now I check the trunk lid every 3 weeks or so. Anyone else have a cover that turned out to be the problem instead of the fix?