Some dogs just don't feel comfortable in the car. The only advice I have would be to stop putting him in the trunk, and start putting him in a crate until he gets used to being in the car if possible. When he get's a bit older I'd probably invest in a dog seatbelt for him unless he calms down and behaves in the car by that point. Besides that, I really have no advice as my dogs have always taken to the care relatively easily.


And now that I know what sort of "trunk" you're talking about, you could get a metal barrier to put up in the back so he can't get out of there. Lots of people do that with their dogs.