4Climber
New member
I have 2 methods:
Exterior (water-sprayed surfaces): Amsoil Metal Protect HD has been holding up very well here. Resists washing away better than than Fluid Film.
Interior (non-water-sprayed e.g. inside of boxed frame rails, that skinny radiator crossmember, door drains): Fluid Film has been my go-to, but last year I used CRC Corrosion Inhibitor and liked it better...goes on a bit thinner than Fluid Film and seeps into the metal seams, then dries in place.
Amsoil Metal Protect HD seems to be based on Cosmoline. As an alternative, you can look into Cosmoline Vehicle Undercoatings - Long Lasting Rust Protection for Vehicles
Also I found this interesting article about the different methods available:
Different types of Rust proofing / Undercoating types explained: which to avoid and which to use | RTS - Your Total BMW Enthusiast