another possible option if you think A/C will be your only High-power item is to look into a Pro-Pak or similar device.. its not cheap
but its basically what Semi-drivers are using now as many municipalities and rest areas prohibit main engine idling for trucks..
typically a unit consists of a 2 cylinder diesel engine, a belt driven A/C compressor, a coolant loop that can be tapped for Domestic cabin heat, and typically an alternator (usually 12 volt, but can be bought 24)..
this device would give you A/C, heat (if you want it), and enough power to keep your 12 volt system charged and operating your low voltage appliances.. (run an inverter for your TV's, computers, etc)...
the engine in it is small enough (typically smaller than a reefer engine) that it is allowed ot be idled anytime.. and Yes you can run it while you are driving your bus if you wish to run the A/C, and fail to have Dash A/C.
the compressor in it is typically a sanden variant so you can run the appropriate matching rooftop or skirt mounted condensor, and then either a basement ducted, or a side / rear mounted evaporator unit... I believe you can outfit them with the sanden 5xx or 7xx (larger capacity) compressor...
again its not cheap but its an alternative to a rather large genset (for an electric A/C unit you need a large gen to handle the compressor start surge).. or having to let your main engines run...