I have painted many trailers with rustoleum and they all looked great....for about 24 months. Then they looked worse than before the paint.
Painted my YJ 6 years ago with Acrylic Enamel with hardner. Single stage, no clear coat. Materials were about $600 including paint, some featherfill, spot putty, primer,sand paper, scotch brite, tack rags, about a case of masking tape, thinner and reducer.
I could have spent another month sanding and filling, but it is a Jeep, not a sports car.
I am happy with the result and would expect a paint shop to charge close to $3,000 for something just a touch better than what I have.
Carter BBD feeding 4.2 Nuttered 6 banger = 22 MPG Hwy
If it was easy, everyone would be doing it.