Car travel

We were having problems with our puppy Diesel traveling in the car - we have a vectra and took the parcel shelf out, put down a picnic blanket and carpet on top of that but all the time He was either sick or went to the toilet in the car within 10 mins. We tried his cage in there but that was the same. We have a harness for him already so bought a harness seatbelt attachment and my wife and the dog sit in the back and he's fine - it could be the company giving him support or that he's just getting used to it. If any of you have any ideas or thoughts about this let me know.

Cheers,
Niknak