From the 147 Elearn:
On the vehicle 90% of the bodyshell consists of panels which have been galvanized, divided into 70% twin galvanized panels and 20% single galvanized. Both the outer parts and the moveable parts are made completely from double galvanized panels with the sole exception of the roof which is made from a panel which is not galvanized as it is not very subject to corrosion.
Following the galvanizing treatment, the bodyshell is subjected to bonderization, a treatment which washes any grease or surface oxidation from the panels and to painting by cataphoresis, a treatment which is fundamental for protection and subsequent painting.
All joints between bodyshell panels are sealed to prevent infiltrations of corrosive agents."
Hard to see how the 90% doesn't include the one part that it would be most sensible to galvanize, i.e the floorpan (an outer part), but who knows, ELearn can be wrong.