You are correct about the spray can paints staying a little soft. Automotive paints have a hardening agent that you add making the paint hard and at the same time more brittle and it does chip easy. My nephew painted the bed floor of his roll back with automotive paint and hardener. It chipped everytime a chain even touched. On his next truck he bought we bought a gallon of rust-oleum, thinned it some and sprayed the bed floor without adding hardener and it held up extremely well.