THe thing that rots out the cab corners is that they do trap dirt, which in turn holds moisture. It always seems to be a great place as a "catch all" for nuts and bolts, tools, rags, etc, which all can lead to moisture issues. The best thing you can do is to clean those cab corners out once and a while. When you park the truck for the winter it would be a good idea to make the cab corner cleaning part of your "winterizing" on your truck.
