I've posted a fair bit about corrosion management and long term tests and have tested quite a few different solutions. Rust Check, Krown and Fluid Film will wash off in an hour or less of heavy rain/driving so I no longer use them on vehicles.
The best I've found for longevity is Mike Sander's Grease, but you need to apply at 100-120 C (over 225 F), which is a PITA. My favourite now is Noxudol 300 and 700, which is a solvent free wax type application (never hardens) which actually contains a number of chemicals that react with rust. It's what Toyota, Izuzu and Mitsubishi have used in their frame recalls for about 10 years. It's about $20 a liter, and only needs annual touch ups. The 300 product is black, and designed for exposed chassis. The 700 is clear, for inner panels and non-exposed areas. Zero smell, stays on, and is one of only two products I've found that actively manages rust with added chemicals. It's easy to get in the US directly from Noxudol USA, not so easy here in Canada.
Noxudol 300/700 sets up in a day or two and does not drip after that. Noxudol "won" this three year long term test by Classics Monthly:
https://www.auson.se/wp-content/uploads/2020/03/rusttest_noxudol_700_classic_monthly_uk.pdf
From one of my posts on Noxudol:
A bit of research on the product yields this:
http://www.google.com/patents/WO2011120646A1?cl=en
According to one embodiment, a composition containing sulfonic acids, petroleum, overbased calcium salts in an amount of 10 to 30% by weight; fatty acids, tall-oil, polymers with isophthalic acid, pentaerythritol and tall-oil in an amount of 10 to 20% by weight; paraffin waxes and hydrocarbon waxes in an amount of less than 10%; base oil, distillates (petroleum), solvent- refined heavy paraffinic materials in an amount of 40 to 60% by weight, each percentage being based on the total weight of the wax component, may be used. This material is available as the commercial product Noxudol 700 from Auson AB, Kungsbacka, Sweden. This material is of waxy appearance and includes a liquid paraffin component.
A bit more research:
Sulphonic acids - rust cleaner
overbased calcium salts - oil additive to prevent rust
pentaerythritol - referenced in several corrosion inhibition papers.
polymers with isophthalic acid - referenced in corrosion resistance material
tall oils - used as a base for corrosion inhibitor products
We're at year 2 for our Highlander and the Noxudol 300 is holding up extremely well. Only very minor touch ups are needed once a year. Our winters feature salt, sand, and temps to -35 C.
