They actually have smaller roof mounted A/C units other than the 13,500 and the 15,000 BTU models.
I always thought if I was to add a second air conditioner to the 5th wheel i would go for the smaller one for the bedroom area that would run from the 2KW Honda setup. That would be my PLAN B for A/C...
I think those portable a/c units that have hoses that connect to windows are also available in small enough sizes to run from a 2KW generator as well.
Also out west where the humidity is low they tell me the roof mounted evaporator coolers work pretty well too.