I have an inboard LP generator 2500. I love it to make coffee, espresso, air drying, recharge batteries, especially if I use the furnace in cold wheather and recharche the computors when boonducking.
For AC, this is another story. Mine will run the AC when it is not too hot! When it is hot, like around 95 and up, the AC needs too much power for restart and the gene stop working. I guess I would need something like 3000 watt.
As for how much propane, I never calculated but the gene is running full blast when the AC is on, so I presume it will suck up the propane pretty quick.