Ah... the dreaded , rust never sleeps , post.
If you can afford the chem dip proceedure , great.
Or try a gentle abrasive like soda blast, cleans really well.
Bottom line is , you've GOT to get ALL the rust first time or it will come back to haunt you!
Just sanding is normally not enough. The metal has to be clean/bright and sanding doesn't get the stuff out of the bottom of the pits. Chemical clean or blasting does.
