A number of years ago we had a 7 day power outage at home, I ran my furnace, freezer, and fridge, off our Honda 2000i. At the time I heard of being able to add an auxiliary gas tank to the unit. With the heat on out west I thought this might be worth posting.
The Honda 2k get 3.4 hours run time when running at it rated load, which is what you'd be doing running your A/C. Here's a Utube video on how to add the extra tank, there are many variations of the setup. I added one and tried it out, it works as advertised. Of course we haven't had an outage since I put the extended tank together.
They sell complete kits, or you can do it cheap like in the video.