POR15. Stop the cancer. Apply front and back. That was the first thing to come to mind. The other thing is FLuid Film. Fluid Film has some products we use on snow equipment to neutralize road salt, and also products to coat equipment between storms or after the season. Once the rust has started it is tough to stop.
This is a tough one. Best you can do is slow it down. Keep it oiled up? Is it designed such that it holds water? If so, you could drill a weep hole? I doubt it is failing to drain.