I agree with Drew. We use bedliner all the time even on very old trucks but only on newly blasted and properly prepped metal. If you have not done that you are better off just cleaning it every so often. The cheaper coatings will absolutely absorb moisture and will cause you problems down the road. Not an implication of 3M products, just an overall observation.
Personally I will cut every corner possible except where hidden rust is a concern. To me that is the best way to really preserve a vehicle.
Good luck.
