What did the paint shop actually do for the 400 quid? Once rust has got a hold is got to be treated somehow either chemically or mechanically.
Nothing to do with the rolled and wired edges, I'm just in the middle of preparing for paint a pair of circa 1985 steel wings which were fitted to a car parked up in a leaky shed since 1993 and they are perfect, no corrosion anywhere. Wired edges and seams still as good as the day they left Eva Bros!