I live in the rust belt. Our roads might as well be made of salt, or whatever corrosive chemical they use to melt snow.
All four doors have the lower outside showing rust damage.
Last year I used a rust modifier and then primed and painted them. I was hoping it would stop the rust but after the winter, the rust is looking as healthy as it did before I worked on it.
My attack on rust on my old 86 Chev K10 was to cover exposed metal (frame, brake lines, supports, etc) with mineral oil. Stopped all rust action and super easy to apply.
Where there are pinch seams I put the mineral oil inside. Once the mineral oil is on and in the rust, water cannot get into it to start rust again. This treatment lasts a couple years then do it again. Makes the ugly rust area turn dark and actually looks good. Stops the rust right away. I have had to replace brake lines twice before I coated them with the mineral oil. Ya got to stop the rust.
The door treatment on the Liberty is going to go a bit differently.
My plan is to clean the surface rust off, prime and paint. then I want to cover that lower portion of door with truck bed liner, reinforced with fiberglas cloth. The truck bed liner will saturate the cloth and even if the door metal does rust away, the liner should be strong enough to outlast the Liberty body and frame.
We are at a point that replacement of the doors is getting to be difficult. The rust belt here has no good doors and you have to choose from the best ones you can find and go from there. Might as well repair the ones you have.
My take on the door rust.