How long do you expect them to stand for? Cosmoline is the original corrosion preventer. Soluble oil in your machining coolant provides some protection after machining. I have found film forming additives used in diesel engine coolants can provide short term corrosion protection without oily residues.

To remove corrosion a quick dip in phosphoric acid will remove light corrosion. Follow up with a rinse in water treated with the aforementioned diesel engine coolant treatments to prevent flash rusting as it dries. The diesel treatment is a supplemental coolant additive or 2000 series coolant treatment mixed 16:1 with water. The active ingredients are sodium silicate, sodium borate, and sodium nitrite. I'm sure there are specific products for your application but I have these abundantly available and they work for me.

These are stainless steel castings. The rust spots are either from small surface inclusions from casting or where you have touched them with steel. Lifting or resting them on steel surfaces will embed small amounts of Fe in the surface which will later rust easily.
If these are only on the cast surfaces maybe you should have some words with you supplier. The casting should have been annealed, blasted (usually grit or shot) and then passivated (hopefully in Nitric acid). The raw castings should never show rust spots.
1. If you have done any machining make sure that you coolant is well filtered.
2. If you do any 'touch up' with wire brushes, flap wheels, or files make sure that these are only ever used on stainless steel. (and make sure that the brushes are 3xx SS)
3. You can remove Fe easily with acids, the safest is a product called CitriSurf which is citric acid based. (I have bad experience with a quick dip in anything other than nitric acid, but that is more difficult)
4. Any of the corrosion inhibitor companies will sell Rust Preventive (RP) oils some of which are designed for Stainless Steels, ask.
5. Use nylon slings for lifting, rest only on wood, cardboard, or plastic, use flange face covers (also minimizes mechanical damage). No chains, no metal forks, no steel tables or pallets.

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P.E. Metallurgy, consulting work welcomed

Ed, if I may ask, how many times have you responded with the same answer to questions very similar to this one? Daily? ;)

Best regards - Al

No, only once or twice a week.

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P.E. Metallurgy, consulting work welcomed

It was a common problem years ago when I worked : A manager would call and say " the stainless you told me to get is rusty and we have not yet used it". I am surprised it is still common.

Have you considered dehumidification for your warehouse?

Install silica dsumidifiers and spray an anticorrosion vernish on your valve bodies

luis

If the cast SS parts are showing rust spots it isn't because of humidity, It is because something was done wrong before.
Storing in dry air will hide the problem, but when they get to the customer they will have rust spots.
Find and fix the root cause.

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P.E. Metallurgy, consulting work welcomed

Have the castings been annealed? Tip, they should be.
Were they pickled afterwards? They should have been in Nitric Acid/HF.
Avoid contact with and steel, or accept that you will have to acid passivate to clean them before storing.

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P.E. Metallurgy, consulting work welcomed