My insurance runs about $800 per year. I drive it year round so I do not know about turning the insurance on and off.
There is one fuel tank but you can fill the tank from either side or both sides. At truck fuel stations, they have hoses on both sides if you want to use them. I just use the driver's side most of the time. At a truck stop, the fuel fills very quickly so I do not need to fill from both sides at once.
Yes, you can run the generator and run the air conditioner when you are going down the road. If the generator is a diesel generator, it will take fuel from the main tank. You will also see some older coaches with propane generators.
There are a lot of threads on the mileage that people get. There is quite a range. I would say 7 - 9 mpg is common but do a search of the forums and you will get a lot of good information about fuel mileage.
