Good luck on your project. Get rid of as much rust as you can find even to the extent of replacing metal. I've spent the last 14 months on my 83 FSB doing just that, hope to finish some time this Summer. Every time I think I have it all taken care of I find another little place it has started. If you do a good job, it will be a few years before you find a rust spot again, but one thing is sure, rust will never lose the battle. In the words of someone I can't remember, "Rust never sleeps". I can't think of many areas of the US, outside of a desert, that wont encourage rust, especially like the North East. The minute I relax, I find it creeping up. If you drive it on the road in, any but ideal conditions, you have set the clock ticking some place on the vehicle. You will need to be on constant vigil for rust no matter what you do. Sounds negative, but it is true. Water can seep through the tiniest hole in your armor. Last week I noticed two pin head size rust spots on the front fender where the inner fender and outer skin touch. You wouldn't believe the amount of rust that was under there, "the top of the iceberg", so to speak. I had to remove the fender and cut all the welds to clean it up.
I have done some drastic stuff on my truck in the battle,like metal replacement, cut welds to clean up seam rust, borrow a section of a 95 tub, etc., but I expect rust will raise it's ugly head again. As far as coating, I have treated all the areas I can with rust inhibitor, sealed, painted, undercoated and in some cases sealed the undercoat with paint to give it a harder surface.
Don't be discouraged by my post. Just a reality check and hopefully aid in temporarily winning the rust battle. Just keep in mind, if you keep it on the road, you will need to be constantly on the lookout.
Good luck,
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