Years ago I had a Dutch Star that had only one AC and it had 30 amp service.
I added a second AC unit positioned using the rooftop vent in the kitchen.
I ran the electric supply romex cable down the refer vent into a storage bin.
To use the second unit I simply plugged into a second dedicated supply at a second outlet at the campsite, usually a 15 amp next to the 30 amp outlet.
The second AC unit had its own set of controls in the overhead part of the AC unit.
Using this method I did use both AC units at the same time because the second AC was the only thing on the 15 amp circuit.
I hope that answers your question.
Edit:
I thought I would add a few more comments.
The 14 X 14 common size roof vent will accept most all roof mounted AC units.
The non ducted or maybe I should say the ones that blow down directly into the room have the controls mounted on them and do not interface with your thermostat. Therefore you can use either or both at the same time.
Good Luck.