Would tow hitch cover prevent rust?

My trailer hitch gets surface rust because of Oregon's liquid sunshine.

Would a tow hitch cover like this one help prevent rust or do it worse by restricting airflow and allowing water to stand?

 

Is the surface rust on the inside? If so then adding a cover will cover it up (out of sight out of mind) and probably restrict a little airflow. But I don't think it'll add any rust.

 

Bare metal makes rust.

Keep the metal painted. If you use anything metal in the receiver (hitch, hitch pin, etc) and scratch the paint to metal then it'll rust there regardless of being covered.

It won't make it air and water tight.

 

Yeah, paint got scratched when the pin was in, which is normal. I coated it with grease for now.

 

I know this is an older thread but my search for receiver hitch came to this. I had that very tow hitch cover and recently lost ("stolen") and new to me I have some rust there. Thinking of painting with rattle can black. Should I sand the rust off first?