I'm with Paul. Your recurring problem stems from not getting the culprit, you're just cleaning the visible part. I also like Rust Free. The main complaint I have is I can't get it locally without having to buy a "kit" that includes T-9 and a cleaner, both of which I find pretty useless.
Take care and read the directions on the Rust Free. It is an acid and you can leave it on too long. Wear gloves. It is great for getting out those shadows that just won't sand out or 'go away' with other methods. I think it will take care of your perrineal rust as well.
For protection I use Johnson's Paste Wax as others have described. I buff it out after it just starts to fog. I do a couple coats and re-wax several times a year (as in 8 to 10).
For maintenance I wipe off the old wax with mineral spirits a few times a year and re-wax. If I have been extra neglectful I put a gray synthetic abrasive pad on a 1/4 sheet sander and work the mineral spirits around with that. I have a cheap little Makita that I reserve for just this duty when required. After cleanup, re-wax.
Any sufficiently advanced technology is indistinguishable from magic.
- Arthur C. Clarke