Re: generator size
Look at it this way: is the trailer 30 amp or 50 amp? If the trailer is 30 amp, then anything over 3600 watts is wasted, because the trailer can't handle any more wattage (30 amps x 120 volts) anyway. So 3500 should be adequate. If the trailer is 50 amp, then 12KW would be the MAXIMUM you would need, but in reality, 7.5KW is generally plenty even with 2 AC units. Less then that is certainly possible, but starts to require you to be more carefull of what you use, electrical load wise.
I suspect 3500 will run most single air conditioners. If the AC won't start reliably on 3500, install an 'easy start' kit in the air conditioner. This is a capaciter which is charged up and a relay, to add the capacitor to the start circuit to give it an extra initial 'kick'. On my 25' trailer, it allowed me to get by with a 3000 watt generator which could not kick over the compressor when it had 'rested' in a particular position for a while.