Honestly, the best way to prevent rust on urban trash bins in rainy climates is to design and maintain them for wet conditions. Start with a corrosion-resistant body—stainless steel, aluminum, HDPE plastic, or galvanized steel with a good powder-coat or epoxy finish. Avoid bare mild steel, and use stainless or coated fasteners so you don’t create galvanic corrosion between different metals.
Make water leave the bin quickly. Add drainage holes, slope the bottom, raise the bin slightly off the ground, and keep the lid fitting well so rain doesn’t pour in. Don’t let water sit in the base or collect around the wheels. In public areas, clean out wet waste and standing water regularly, and let the bin dry when possible.
For existing bins, wash off dirt and salt, remove loose rust, apply a rust converter, then prime and repaint with a suitable enamel or protective coating. Touch up scratches and chips quickly, because small breaks in the coating are where rust starts. A coat of rust inhibitor or wax on exposed metal can help, but it needs reapplication.
Finally, schedule inspections, especially after storms. Check welds, hinges, drain holes, and the bottom for trapped water. If a bin is badly rusted, replacing it with a better-coated, drainable design is usually cheaper than repeated repairs.