I have an Onan 2.5 in my TC. I wouldn't have ordered it that way but I bought used and it had one. I use it for the microwave, coffee maker, toaster, etc. It's very handy: starts right up, nothing to get our or put away, and no need to mess with gasoline.
I don't know how much fuel it uses but I've never run out with 2 20# tanks. I can't imagine running it non-stop for the AC. If I'm camping when it's hot I go somewhere with electric. I like to camp out in the middle of nowhere but I generally do that when it's cooler.
I have run my gen. for 6 hours at a time powering my house during a utility outage. It started on a less than full tank and never switched to the other one.