Rust on bearings is usually the result of a chemical reaction between the bearing steel and moisture. To prevent this from happening, you must either: 1. Have no moisture present; 2. Use bearing materials not ordinarily capable of rusting (300-400 grade stainless steel, plastic, or ceramic); or 3. Somehow prevent oxygen from getting to the bearing steel.
The most practical method is usually #3. There are many methods to accomplish this including plating, special phosphate coatings & oxides, surface treatments, and many variations of each. None of these processes will stop rust forever, but rather may delay its start or slow its growth.
Grease, oil, CSL-EP, and CSL-EPN will all, to some degree, slow the growth or start of rust. Regular CSL, however, has no liquid in it and a bearing processed with CSL may be more prone to rust in high humidity applications than the same bearing with grease or oil.
High heat will make bearings rust even faster. In this case, CSL-EP, CSL-EPN, or Cobra Blue surface treatment may be an effective product to slow the start or growth of rust.