I did petty much what Marc described.
Wire brushed, swept, sprayed Prep and etch.
When that dried out, I found a chalky residue left on the floor. With a little effort it came off. I wire brushed the floor againand swept. Then I cleaned the floor with a TSP solution.
Then I rolled a good coat of Rusty metal primer.
Next will be covering all of the screw holes with adhesive flashing from Home Depot. Then I will roll a coat of Rustolium paint.
Many way to skin a cat