Thanks for the replies so far everyone - they've certainly helped me understand this better. Or at least I think so.
dahkota - Water heater is off.
dclark - Neither AC runs if EITHER generator CB is off (see my troubleshooting steps below)
dougrainer - Your info was particularly useful. I did some troubleshooting and found the following:
With only 20 amp generator CB off:
Both AC units have no power
All outlets have NO power
No coach lights
Slide does work
With only 30 amp generator CB off:
Both AC units have no power
All outlets have power
No coach lights
Slide does work
Possibly unrelated: When one of the generator CBs is off (I forget which one) the "levels" button works and shows me tank, propane, etc levels. When the other CB is off, it doesn't. I only mention it because I wondered if power is being turned off to the thermostat (since it's in the same overall control panel) and that could be causing a problem. Again... new guy here... so might be completely off course.