Remove the tub to a good working location. Place the tub on painter's drop cloth.
Place duct tape around the curved top edge of the tub to protect the porcelain interior of the tub from sanding along the edge.
Grind and sand with an orbital sander or grinder. Hand brush small areas with a wire brush and scrape off any loose paint. For tubs in bad condition it may be necessary to have the exterior of the tub sand blasted to remove the old paint and rust.
Mix and apply bondo to areas of pitting. Smooth out the bondo using a putty knife. Allow the bondo to dry and then sand down the finish with a sanding block or sand paper.
Wipe the entire exterior of the tub down with Willbond deglosser using rags.
Prime the entire exterior of the tub with a rust preventer-type primer using a disposable paint brush. Make sure to prime all of the surface and to seal the metal to prevent future rust. Primer sticks to the metal and the paint will stick to the primer so a good primer coat is essential
Paint the exterior of the tub with three coats of a quality paint using an angled 2-inch paint brush. Oil paints are preferable. Allow the paint to dry well between coats.