Steve,
I too am interested in rust prevention and would also be interested in any opinions forum members might have?
I have always been a bit sceptical about magic paints which claim all sorts of rust killing properties but FWIW ..........
The POR-15 anti-rust primer has been around quite a while and I have read lots of positive comments (often from the States)...... From what I understand it has two major drawbacks
1. If exposed to light it will break down and ultimately fail so must be overcoated to protect it
2. It needs an etch primer to allow the top coat to adhere to it properly. This adds to the cost of a fairly pricey product.
There is another product from the USA called "Rust Bullet" which claims better protection and longevity than POR-15 and is also stable in UV light so doesn't need to be overpainted. The test results on
www.rustbullet.com do look very convincing.
Both Bullet and POR claim that they work on already rusted steel by bonding the surface into a stable structure which will not flake off and more importantly, will not rust further.
The main drawback I can see with Bullet is that it is again quite pricey and the only UK supplier I have found seem to be "out of stock".
www.rustbullet.co.uk/shop/index.php?act=viewCat&catId=3
If anyone has tried "Rust Bullet" or any similar product I would be interested to know what you think?
The Dinitrol wax products are widely used and generally accepted as an effective way to at least slow the progress of rusting. They (and Waxoyl) work on the same principle as a greasing or oiling steel. They form a sticky barrier which blocks oxygen and moisture from the surface of the steel and thus impede the rusting process.
Back in the seventies I knew a chap with a Mk2 Cortina who used to put his waste engine oil in his sills - That Cortina had the most immaculate sills I've ever seen

.......... but his driveway was a bit of a mess
Again FWIW I have used quite a few of the so called Zinc rich primers and am not really convinced they offer much over any decent coat of paint.