You will get a number of different opinions re safely transporting dogs. Ours is we wouldn’t recommend your dog travelling in the rear, they are too far away from you and very vulnerable if you unfortunately have someone go into the back of you. Similarly we wouldn’t recommend canvas crates they are not crash tested and don’t offer any protection should you have an accident.
When older we would suggest a good quality harness attached to the seat belt. For a pup it’s a little trickier you are probably reduced to a crate short term. Make sure it’s of good quality with escape doors front & rear and securely anchored so it doesn’t move. Use it in the house first, leave the door open put some blankets, toys, treats in it to encourage the pup to use it. Then gradually put it in the Cali but don’t go anywhere just let the pup get used to it. Slowly and patiently is key to having a dog feel safe and comfortable in a vehicle. Looking forward to hearing your progress.