Cosmoline is a good product that doesn't get enough recognition.
IMO, an oil-based, creeping/self-healing is the best by far.
Fluid film, krown, wd-40, or even used ATF are all superb. In a sprayer and properly applied, you can keep any truck pretty much rust free with not too much time invested by treating your undercarriage with one of these. Personally I like fluid film because I think it's a bit better for the environment than ATF or wd-40. Krown is probably similar but haven't used it.
That being said, any treatment is more environmentally friendly than scrapping your car due to rust and the idea is that the majority of it sticks to your frame anyway.