I think that the rust is generally cosmetic but the worst should be limited to deeper pitting. According to the dealer the rocker panel is a one piece unit and if damaged or severely corroded the recommendation is to replace the entire unit to maintain structural integrity. This must be a very expensive choice!

After talking to a few hotrodders it appears that the best option is to use POR15 "silver" which can be used as a bit of a filler if the area is badly pitted. So I've ordered the starter kit and I'll wire brush the area and use the kit to clean and cover the rusted area. I hope that there will not be any compatability issues between the surrounding metal and paints with POR15 - anyone know?

As this area of the car has an undercoating - is it effective to blend the repaired area with the rest of rocker panel? Or should the entire rocker panel be redone? I presume that the undercoating material is still available. Would this be a specialist application?

Thanks,
Paul