Avoid moisture/water sitting on the tractor/implements as much as possible (including too frequent washing ) & you'll limit rust. Moisture+Oxygen+Steel=Rust
Minimise the H2O &/or Oxygen contact with the steel &most of the rust problem is solved.
We only throughly clean farm equipment Twice/year with a pressure washer, always then dry with high pressure air &/or lawn blower & depending on the equipment area/paint finish immediately coat with a solution of sprayed wax &/or lanolin. Between these biannual washes the equipment is only ever blown 'clean' with compressed/blown air. IMO washing too frequently & over enthusiastic pressure washing forces:
- moisture into areas of equipment it wouldn't normally or regularly access
- same for washing detergents/cleaning solutions (which also contain high levels of nitrogen/phosphorus, known rust 'enhancers' if they lay in combination with water on poorly finished equipment areas)
The underside of equipment we treat annually with the marine rust inhibitor 'Penetrol' - as it always remains a slow moving fluid keep well clear of all gaskets, seals & bearings as it will degrade them.
This routine preserves our equipment & generally rust free despite regular exposure to fertiliser, sprays/chemicals & the other equipment hazards in a commercial farming operation.