An outdoor gym in India has to survive monsoon humidity, summer heat that softens cheap coatings, and salt air if it is anywhere near the coast. The equipment that rusts within two years almost always failed at one of three points: the fasteners, the coating system, or the bearings.
Use marine-grade stainless fasteners, not zinc-plated ones. Zinc looks identical on day one and is orange by the second monsoon. For the frames, a two-stage powder-coat — zinc-rich primer under the colour coat — is what stands between the steel and the weather; a single decorative coat chips and lets water straight in.
The moving joints are the last trap. Sealed bearings cost more than open bushings but they keep grit and water out, and grit is what actually kills an outdoor rotation joint. Spend there, and the equipment is still turning smoothly when the paint is the only thing that needs attention.