First, move to the desert...
Proof that dampness causes corrosion is seen in the FIAT 124 Spiders that exist in Arizona. Twenty years after their counterparts elsewhere were rusting merrily, these cars are pristine (if a little faded!)
Keeping the metal dry is the key to success. That means a non-porous, water-repellent coating. The moment the factory stone-chip coating begins to flake away, it needs to be removed completely - otherwise it will just hold water against the metal.
Rust-proofing measures need to take place when the car is completely dry. E.g. inside the doors, the seam sealer along the bottom of the door frequently needs a bit of 'help' as it gets older, cracks and shrinks. I use a spray-on wax for these areas. I spray inside the sills from the round holes in the inner seals (lift the carpet back first).
I find that rust-converting paints that change colour from white to blue to black (I think Kurust is this type) are only a limited success. The rust still continues underneath its new black coating! Acid-based products do sometimes convert the rust back to steel, but it is difficult to control the process - the steel turns back to rust again if there are acid residues around!
It's best to just remove the rust first using a wire brush on an angle grinder, or even just chipping with a screwdriver. I believe that the black fibrous 'strip-it' discs are effective. After a bit of practice you learn about the different types of rust - thick and flakey orange, thin and hard black... it's best to continue until there are only tiny black residues of rust which cannot be chipped off and which the rust converter will probably bond to.
Any sort of coating before the rust starts is effective. E.g. where there is a stone-chip to clean metal, just fill it with the topcoat paint as soon as possible. You can get away without primer this way. Once the rust starts, it has to be sanded-out, filled, primed, etc.
Another type of treatment is what I call 'damage limitation'. E.g. if there are some small rust holes forming behind the rear bumper, or in the bottom of a door frame, I would clean up really thoroughly with the wire-brush attachment, then paint with etch primer, and 'proper' topcoats to a glossy finish. I wouldn't actually fill the rust holes in this case, since filler (and other materials) tends to end up trapping water against the metal in the long term. 'Clean' rust holes, painted, don't grow (in my experience). As a compromise for where you have to fill the holes (for cosmetics, or to avoid suspicion
) I would only fill over etch-primer - not directly to the metal. I know that most fillers say not to do this in the instructions. But it works fine.
The seals along the base of the door windows tend to shrink. I swap the seal from the inside to the outside (the retaining strip is released from inside the door). It all helps to minimise the amount of water that gets into the door.
You could talk about rustproofing for days with the Uno, but basically the essence is to remove flaking coatings, ensure metal is clean and dry, and re-coat with the best materials you can...
-Alex
