I might take a photo of the run of clips along the outside here later on, the nail heads are just a large red rusty lump. OK they are still holding but it's only a matter of time before they do fail and removal will no doubt cause spalling at each one due to the expansion.
Anything "ordinary steel" outside here will be seriously rusty within
5 years. The quality of galvanised stuff is very variable, some things are just as installed (but not many) others are rusty.I'm of the "if a jobs worth doing, it's worth doing properly, once".