Galvanised surfaces can still corrode unfortunately, and abrasion can remove the zinc coating from the steel.
One side reacted fairly heavily to the rust neutraliser and the other had a much smaller reaction, I resprayed with graphene primer and put a bit of underseal over it for now, but will be going back later and adding better protection. Probably that helicopter tape Jace recommended.
I considered something like dynamat sound deadening but concern that the bituminous material could hold moisture.