More info: The power was completely off (12 and 120 V). I had already removed the cover. I was just looking at the existing breakers. I have in the past replaced house breakers so I was just considering how I would do it in the trailer.
There are currently 3 double pole breakers and I will be adding a breaker for the new converter. Just for my own knowledge I did try removing one by rocking it but there is a plastic divider at the end opposite the conductor terminal screw so I couldn't really grab it well. That is why I thought there might be something I was missing.
Thanks for all your input.
Mike