when getting ready to run film, shut off generator and run off battery back up.
shot done, kick on generator.
If you calculate the load you REALLY need to run. (a camera, a few LCD panels, small audio gear, laptop...) it might come out to well UNDER 300w and hence you'd get that much more time between generator running.
(create your own battery bank from deep cycle marine batteries and a power inverter to drive 120V loads)