Can anyone tell me if it is safe to use Rust-Oleum on moving undercarriage parts (like the driveshaft for example)?

Also regarding the undercarriage, should I spray it on or roll it on? And should I first apply Rust-Oleum primer and then Rust-Oleum paint, or should I skip the primer and just use the paint?

I'm in the process of painting an old school bus I'm turning into a camper. The upper body is pretty decent for being 20 some years old, but the undercarriage has quite a bit of rust.