Advice for refinishing inner fenders and battery tray

[1967C20]

These are my inner fenders and battery tray. This truck is a driver and I wanted to freshen the doghouse while I had it off for a front end rebuild. I want it to look nice but I would rather not have to take it all apart either. There is some moderate rust under the battery tray where the core support and the inner fender bolt together. The battery tray looks bad but is actually pretty solid. I need advice on paint: POR-15, Rust Bullet, rattle can black, other? Can I get a smooth finish by brushing on the rust paints or will I have to spray? Either way, I see a lot of sanding in my future.