I usually buy the smaller kit each year. It's enough to treat the various rust issues that I have to deal with. A little goes a long way, and I'm not sure what the shelf life is.
Rust is a way of life here, I have a 2004 F-250 that already has its fair share of nicks and bruises. Without the yearly oil treatment it would never last more than ten years.
Regardless, we accept rust, and the passing of our favorite vehicles as a way of life. Maybe that's why we drink so much...

__________________
Pure Vermont Maple Syrup
http://www.squaredealfarm.org

1982 300D Turbo
1983 300D Turbo

Ha! Two weeks ago I looked at an 85 300TD that was covered in rust. It was hard to stomach and if my car turns into that I will definitely be drinking a lot!