I'm in PA same thing here not a spot of rust only a little paint rub at the top of bedrail.

 

I think it depends on how you use your truck maybe as to how it affects the bed under the liner. I had a liner in my Dakota for years. The guy who bought it checked under it and it looked good as new. I never hauled anything though except the occasional load of mulch or washer appliance. I also had a tonneau cover on it.