Scurvy, I truly have never considered painting a trailer with it. And I have no clue. I will recommend something generally if I KNOW it will work, but without actually trying it, again, dunno man.
But, I don't think I would do it. To many metal paints out there that are perfectly suitable for the job, and just guessing again, this doesn't strike me as a decent choice.
The one time I painted a trailer, (if you can call it that), I used a cold galvanizing spray paint. I have actually used this stuff on several occasions in the steel business, with very good results. And if I had to do it again, I think that I would be inclined to use the same stuff.