Portable generators are horribly inefficient. At 110 volts a tesla charges around 2-3 mph. A small 2k inverter generator goes maybe 4 hrs at full load with a 1 gallon tank (1500 watts continuous, 20 amps max, this is slightly less power than an outlet in your house).

Electric cars typically need to be grounded to charge, so even if you were able to bypass that, your electric car will get less than 8 mpg if you were to charge from a generator, probably closer to 5.

Carrying 20 gallons of gas and a portable generator in an electric car will give you around a 100 miles of extra range, maybe 150 tops. It will take 2-3 days to charge it, which will also put you several hours past the scheduled maintenance of the generator.

If you want "huge" range from gasoline, it's better to get a small car that runs on gasoline. The idea that you can power an electric car off a portable generator is retarded