Except that with the covers in place, the moisture that is causing the current rust will be trapped, and further accelerate the rate of corrosion.
Somehow, those rusted latches are being exposed to moisture, or were exposed to salt or some other corrosion-inducing chemical:
- Cruising along the water's edge at the beach, or driving through deep brackish water?
- Kids hopping in back while dripping with salt water from the beach?
- Exposed to road salt during the winter?
- Kids spilled soda or lemonade on the floor?
- Driving on dirt roads near Ouray during the Summit, right after they were sprayed with magnesium chloride solution to hold dust down? I was horrified to see that some of the dirt roads around the B&B we stayed at in Ridgeway were HEAVILY sprayed with mag chloride every morning for several days in a row. Couldn't help but drive through the corrosive slush to get to the Summit meeting points, and they didn't put up the orange MAG CHLORIDE signs until later in the day.
I'd take the latches off, clean them thoroughly with hot water and detergent, coat them with some renewable corrosion inhibitor (LPS-3, Boeshield T9, etc.) and then try to find out how they are getting wet.