Comfort is key when it comes to concealed carry, particularly while driving. Seatbelts can add pressure to your firearm, causing discomfort and potentially revealing your weapon. Select a holster designed for comfort in seated positions. Or, if needed, use a car gun holster while driving; you can find examples at https://www.setick.com/best-car-holsters/.
In an emergency, you need to access your firearm quickly and efficiently. Choose a holster and carry position that allows easy access without compromising safety, such as a cross-draw holster.
It's one thing to draw your firearm from a holster while standing and another while seated and buckled in. Practice drawing your firearm in a safe, unloaded condition while in your car to ensure you can do so quickly and safely if need be.
Laws governing concealed carry while driving vary significantly from state to state. Some states require notifying law enforcement officers immediately if you're pulled over, while others do not. Make sure you're familiar with the laws in your state.
If you have to leave your vehicle and enter a building where firearms are prohibited, plan how to store your firearm securely. A lockbox affixed to your car can provide a secure storage option, but there are other alternatives. What's important is that you should never leave behind an unsecured firearm.