So my Duster is mostly Rust Free...

Might I add, be careful leaving Ospho on any chrome or stainless for any amount of time. Wash it off or if you get it on there, be sure it is neutralized. I would apply Ospho to that inside of roof also, once to sanded it best I could. I have used and like BodySchultz for decades. Probably a pre runner of maybe bed liner?. A great undercoating. You can find a gun for your compressor to spray for cheap if you look. Make sure your air pressure in NOT too much, don't ask me why I know. I would also spray it with a good epoxy primer, before the undercoat. I hate doing headliners, and don't go there anymore. But I am not a car show guy.

If I ever find a pro body guy that recommends a "rust convertor" , then I will use some. JMHO