Hi Dave,
Although I have not used any rust preventative paint as yet I have been investigating this product.
http://www.ppc.au.com (por15) Very expensive stuff though and the metal preparation must be spot on.
It is very difficult to decide which one to use as the manufacturer is trying to sell their product to you and of course will say it the best thing since sliced bread. ( They sent me a restorers catalogue for free, fill in the details on the site and it came in the post)
Have been doing web searches for por15 and it shows a lot of restorers and old cars, vintage stuff and things like old landrovers being done so I suppose that is good enough for me.
On the ppc site there are real world tests of painted products. Look in the PDF files, it looks like good stuff but it will take you to make up your own mind from both reading about the product and seeing what other people in the same boat are using.
What are people here inclined to use?
Cheers Michael