I started using Fluid Film in the 90's when I worked on a commercial fishing boat. Back then you had to buy it from a Fluid Film distributor, now you can buy spray cans, gallons or 5 gallon buckets at NAPA. It is a great product and quite water resistant, but definitely needs to be re-applied at least once a year. It is similar to oiling a frame and coating it with dust and dirt to form a protective coating to keep OXYGEN away from the metal. Fluid film is lanolin though, with no petroleum in it. Won't harm the environment. Once the frame is rusty, short of sandblasting it and painting it there is not much else you can do, and there isn't really any good way to clean and paint the inside of the frame, so Fluid Film and similar products are the only alternative. They sell a Fluid Film spray gun kit with 2 wands to apply it inside the frame. (you need an air compressor) I buy 3rd gen 4runners with bad frames and repair them to sell, so I'm very familiar with what the inside of these frames look like in harsh environments like we have here in Maine. I can't speak about the other products mentioned in this thread, but I can say that Fluid Film works well and that it is a good idea to drench the inside of your frame with it.