Here's how to use these practice sessions to get your dog used to your being away from him:

Inside your home, tether him to a stable object a foot or two away from you for several minutes. Gradually increase your distance from him over the course of a week or so until you can leave the room without concern.
Once you can be in a separate room, try practicing this in your car while it is parked in your driveway. Secure your dog in the back seat and practice opening and closing your door without getting out until he is okay with that action; then practice getting out and gradually increasing your distance from the car.

It may take many sessions, but remember, this is not like teaching your dog to sit on cue -- this is about changing an emotional response to a stimulus, and that takes more time and effort. But it's surely worth it so your dog will get to share in your travel fun!

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