Camping mode:
To avoid the automatic shut off after an hour, the car has to be in gear
and the driver door cannot open (automatically shifts back to Park). 
So:
1. Enter through the passenger door.
2. Hold down the brake pedal with a stick (I use an umbrella) and start the car.
3. Make sure the parking brake is on, and shift to Neutral
4. Exit through the passenger door.

If you won't actually be in the car, you can turn off the heating and air conditioning system to save energy.
While the car is in gear (Neutral), you'll hear the pedestrian alert sound, 
so you can pull a fuse (Fuse #34 under the hood for 2017-21 Bolt EV, Fuse F10 on 2022 Bolt EUV).