The company I used to work for started powder coating almost 30 years ago. We build packaging machines using a lot of cold rolled steel bar stock and sheet metal.

We learned a number of things over the years in regards to making powder coat stick.
1. Again prep is key. Steel stock is coated with some type of rust preventative and it has to be completely removed. We have a wash bay to clean the metal.
2. Sharp edges knocked down.
3. Don't use lock washers that bite into the powder and crack the powder. That's where the rust will start. Use flat washers and Loctite. When you install the washers most have slightly curved side and the other side has a bit of an edge. Install it with the curved side to the powder coat.

Yeah trailer hitches here in MN almost always rust due to all the salt. I guessing if the hitch was sand blasted before powder coating it would stay nice looking much much longer.

In short...powder coat is better and more durable when done right....prep work and process. Paint looks pretty, shines more and has a vast array of colors. But, isn't anywhere as close in durability as powder coat. True, it's easier to repair. But, that's the thing...you will definitely be repairing it. If you had a trailer queen and 100 point show car, go for paint. With it being a daily driver...powder coat would be my choice.

Powder coat is my vote, that is, for your application.
1. Powder coat is tough and very durable

2. Just like paint.., prep is everything.

3. When sprayed, the powder coating does not like sharp edges so please smooth them.

4. At my local powder coat shop, we:
A. Clean and clean again.
B. Power wash with detergent after we hang it.
C. Phosphate wash for max adhesion.
D. Install thermocouples and place in oven.
E. Heat the part to desired temp as referenced by thermocouples because as you know, oven temp is not part temp.
F. Monitor temps to ensure proper part "bake time" while still bare.
G. Remove and let cool, inspect surface for contaminants
H. Spray powder, cook, and let cool fully before handling.

5. Funny thing, I insisted on paint for my BBC aluminum valve covers so we powder coated them first as a "primer", then block sanded and painted the powder coat. Turned out nice.

6. My two cents..,