A firearm can only be unloaded and encased in a vehicle. So...
To open carry you need to remove the case from the trunk. Take the pistol out of the case with the case not being inside or touching the car, you can load it and the put the empty case back in the car.
Now that you are carrying, there are 5 places you can't carry.
1. Knowingly within 1000 feet of school property, not just a school building.
2. Government buildings.
3. Restaurants that serve alcohol.
4. In a vehicle.
Fudge! I forgot the last 1. Someone will add.