[lupo]

The first thing you have to do is remove the paint. Put on rubber gloves , take your metal prep and a maroon Scotch-Brite pad and scrub the metal prep into the remaining rust. This will dissolve the remaining rust. Then use 4 inch foam roller apply two coats of the moisture cured urethane permanent rust sealer use the silver formulation preferably non leafing. then Prime and paint it. So now you have removed all the rust and left a zinc phosphate film , applied in airtight primer over it there is nothing left humanly possible do to prevent the rust from returning. I hope this helps