Marine paint is fine to use but it's main benefit(cost) is that it is non-toxic to marine life, an experience I hope your Ranger avoids, lol.
After cleaning use Naval Jelly as instructed, that will change any remaining rust to a neutral surface coating.
let dry and prime
Marine paint, as said, is fine but any exterior rated paint will be fine as well, hull paint often doesn't hold up well in direct sun light, some do, but not all.
Primer bonds to metal, paint doesn't
Primer can't hold up to moisture and sun
Paint can bond to primer, and can hold up against moisture and sun, exterior grade.