Just some info:
Is stainless rustproof? Yes and no. It becomes rustproof by the formation of a very thin oxide on the surface (as does aluminium). This is electrically non conductive and hence removes the basis for corrosion. If you scratch it and eliminate oxygen, e.g. keep it under water or oil, to prevent the formation of the oxide, it will rust. As it does sometimes under washers. Certain chemicals e.g. chlorinated products will also cause corrosion on stainless steel due to their reducing nature. If you use passivated Zinc plated fastenings these may prove better as on steel they are sacrificial as the plating dissolves to protect the bare steel.
The idea that stainless steel will neither stain or rust is a myth. The "stainless" in the term "stainless steel" refers to the fact that there are no impurities in the metal itself, and that nickel has been introduced into the alloy to produce a more acceptable finish. A lower grade of stainless steel with a lower nickel content will attract a magnet, also contrary to popular myth.