OP here, and sorry to stir up so much dust on this one, I guess the NEC isn't as clear cut as I thought...
Once again, it's a question of convenience, not capacity. The TT stays plugged in while at home to power the converter to keep the batteries charged, so drawing almost no power. I like having 30a service there for the 1 or 2 times per year I will use the a/c in the trailer.
I like the idea of a 20a outlet on the power pole in case I want to plug in a hedge trimmer or similar. The TT does have an outdoor convenience outlet on it, but it's on the side that faces the fence. Having an outlet in the pole saves me about 25' of extension cord.
So if the TT is running the a/c, that means folks are staying in it, and obviously I am not running a hedge clipper.
Just to be clear, I am planning to install the new box with breakers, and I'm not planning on having it inspected. Although I am a DIYer I am quite knowledgeable about electrical wiring and code requirements. This post was mostly a point of curiosity about whether this installation would meet code or not, it;s not a safety issue since the 10 gauge wires are protected by the 30 breaker in the main panel.