Always line the base to make it warm and comfortable with a vet bed or similar. Begin by leaving the door open and put your puppies toys inside so it has to go in to retrive them. After a few days the puppy will start lying down inside. After the pup has become used to sleeping with the door open, you can close it whilst the pup is asleep. When it wakes up, open the door after a few minuts and give it pleanty of praise as it comes out. Over the next few days, increase the time before releasing and your pup will soon come to accept the closed door and look forward to the praise on being released. NEVER use the crate as a punishment, your pup must associate it as a safe haven with no negative experiences.
I hope it goes without saying, that your dog should always be kept under control when traveling in a car. If you have an estate car then you are in a good position to use a car cage.