Getting rid of Rust

For what it is worth you can sand til the cows come home, there will be rust in the pores of the metal. My car had hours of preventative measures thrown at it prior to painting in an attempt to avoid putting 1/4 patches on it. A few weeks after it was painted a very small bubble appeared. With how little room there is between the 1/4's and extensions there is no way to effectively treat that area to stop the rust, if it is already present. Car is going back to the body guy to replace the lower quarters and trunk extensions. I know I did not answer your question but.......