As was stated, the dual breakers have been around for a good while. Campers that are on a 30 amp 120 V shoreline cord use a 30 amp/20 amp dual breaker. They feed the shoreline power into the output of the 30 amp breaker that then powers up the breaker buss. The breaker will work the same whichever way the power source comes in. The 20 amp breaker is then for the roof AC unit. Dual 15 amp ones feed the rest of the AC power circuits.
Here is a pic of a WFCO power converter with all dual breakers and the 30/20 amp in the first slot. The power converter board died (common on this brand) and was upgraded with Progressive Dynamics.
Here is an older 2004, American Enterprises converter, the same breaker setup.
Just passing this along for those that may not have seen this before.
John