Yes it is possible to carry a gen set and run the AC, most dry campers (without services) have generators. The minimum size is about a 3000 Watt, most RV campers use a quieter, inverter type like the Honda EU3000i, or twin EU2000i parallel cabled together to produce 4000 watts. Minumum current for an air conditioner is 12-14 amps continuous, about 20 amps inrush starting current. At 120 volts this means at least 2400 Watts. Expect to pay near $2000.00 to purchase new.
There are a lot of research and threads over in the Generator section of the forum (Click here).
I doubt the M-21 has a built in factory option so your options are to carry it in the back of your Tow vehicle (truck) or inside the trailer door/storage compartment - it would have to be brought outside to run the generator.
If you only want a generator to charge batteries there are other options for a smaller gen, but you did not ask that question. Please DO NOT just purchase a construction generator (LOUD!!!!) and run these in parking lots or campgrounds --> very annoying with noise pollution.