rust spots on old steel horse trailer

My old steel horse trailer has the usual heavy rust spots especially around door hinges and latches. I want to stop the rust before it gets too deep. I'm more concerned about stopping the rust than the appearance. I plan to paint it after I fix the rust with spray cans. So I'd like your input on the steps I need to take. I'm thinking, sand or grind, ospho, Rinse?, primer, paint. Will this work? I don't wanna do it twice.

The rust is under the paint. If you don't get under the paint and fix the rust it will soon come back. At least take a sander or knotted wire wheel or sand blaster and take it down to bare metal around the hinges. Then prime and paint. A better fix when you go back would be to use epoxy primer and automotive paint. They do make epoxy primer in a rattle can but it's difficult to find. Only an automotive paint supplier would carry it.

Another very effective tool for rust removal is a flap wheel instead of a grinding wheel. After that your plan is very good.

If your purpouse is giving moving parts as long of life as possible with little concern for appearance,don't worry with cleaning rust off,oiling moving parts will add far more life than primers and paint. For frame and sheet metal parts,remove rust while removing as little metal as possible,wipe bare spots with Ospho or similar to convert unseen rust,prime and paint. Do youself a favor and buy a HVLP of some kind. It is prohibitivly expensive and time consuming to build a layer of paint with rattle cans not to mention limited choices of paint. Rustoleum is about as good as you will find unless you invest in PPE for use with advanced paints. If you have ever been on a ship you probably noticed crew walking around touching up paint with brushes.
That's not a bad idea for equipment. I put a hole through screw on caps of 1/2 pint pvc primer cans then epoxied small nylon brush handles in them. Cans contain equipment/tractor colors,rusty metal primer and Ospho.
Very handy when I see something in need of small touch up because the brush doesn't need to be cleaned after each touch up,just screw lid back on with brush inside container where it never dries out.