Thanks for all your input. I went to the storage yard to double check everything. I was able to wiggle the breaker enough to get it to release.
I have 3 tandem breakers currently installed. One pole of the top one is the main at 30 Amp, the others are 15 or 20 amp. There is physical space for 2 additional breakers or possibly 4 more circuits. On the cover that is removed to access the wiring there is the following: "Maximum 9 branch circuits with use of duplex breakers". On a 30 amp trailer, I agree, I would never use all of them.
Since I want to add ONE circuit for a second converter, should I use a single or a tandem which would give me an installed spare?
Mike