I own a Yamaha 2400is and am thrilled with it.? It happily runs a 13.5K Coleman Mach III Power Saver with room to spare.? Each A/C brand varies greatly in power consumption!? The 2400is is very quiet, a fuel miser, and not too heavy to heft around.? It's perfect for a small trailer.? Good luck!
The Yamaha is a nice looking unit with good specs. With a continuous 20A output, it should be able to easily run most any 13.5 kbtu a/c unit, as long as there aren't other loads. About the only concern would be the compressor start up cycle on an older a/c that was laboring to start. That could exceed the Yamaha's peak load of 400 watts. Or most any other 20A breaker.
A Mach Power Saver a/c like Alisstairs has a nice low power draw (around 9 amps continuous) and the 2400is can easily run that and some additional light loads as well.