With regards the quality of the OEM factory disc's, we are a bit stuck with them for now, until some of the third party suppliers are able to provide alternative products.
Here is a company who apply a anti-corrosion treatment to their disc's :-
"Comline range feature a specialised anti-corrosion coating. This coating is applied to all areas of the disc, including the hub and friction surface, to a maximum thickness of 25 microns, ensuring effective rust protection and premium aesthetics.
To achieve this premium finish, each Comline disc is subjected to a nine-stage process that adheres the advanced formulation coating to the precisely manufactured disc. Corrosion resistance is guaranteed by extensive salt spray testing up to 240 hours."
A lot of the trade have had good results from using these disc's.
Of course the ZS is not covered - Yet !.