a garden is a humid environment. Many tent poles are the cheapest, shittiest material possible that will rust through the paint.
stop spraying the poles with anything that can oxidize it, and that will help, but again.. RH% of a garden will make it happe eventually with metal prone to rusting.
rustoleum? LOL stainless steel poles? probably won't see that.
it may not look pretty but will not harm anything either.