I think for a 3 day stay you will find batteries with or without solar to be a far less expensive option than a generator. I have 1 group 24 battery and 1 group 27 battery (It's just what fits). I have a 100 watt solar panel. That's all the power I need for extended stays with no electricity. It won't run the AC, microwave, etc. but it does keep the light, pump, and refrigerator going.
Generators are expensive, particularly quiet ones worth owning. Then you have to buy gas and oil and keep it changed. Do you have a truck or an SUV? If an SUV I wouldn't want to put a gas can inside because of the fumes. If a truck, how will you keep someone from steeling the generator out of the bed.
Just some things to think about. I would go camping a couple times and see how the battery lasts before spending hundreds of dollars on a generator.
You know, you can just plug the trailer's 7 pin into your tow vehicle and run the engine if you really need an emergency charge. That might even be quieter and more fuel efficient than a cheap generator.