I read that somebody once tested to see that the generator plus the rooftop air conditioning consume less fuel than running the dashboard air conditioning by itself. It might be something you might want to check out. I would not worry about the hours on the generator as it is recommended to use the generator frequently to keep it running in good shape. The generator is there and is to be used quite a lot so just use it and the gas consumption is about to 0.2 to 0.4 gallons per hour with the air conditioning on for a 4kw onan.
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