Stain less steel is rust resistant, but not 100% rust proof. Due to the mix of materials, often optimized for high strength, like safety relevant screws for the handlebar or stem, these parts will not be rust proof against sea water. There are a different types of stainless steel on the market, general use, high tensile and specific marine grades.
Unfortunately are the choices when it comes to buy of the shelve OEM bicycle parts limited, marine grade standards haven’t been implemented yet.
We do encourage our customers, when living close to the sea, to mitigate rust by using a thin layer of silicon spray on all stainless steel parts. Just make sure not to get any spray on your brakes…