Thunder Shirts work great for anxiety. You can also take short trips and make them fun for the pups so stop to play or give them treats along the way. You may only go around the block or a mile down the road and turn around. If they're really upset, you might want to just sit in the truck with them and not go anywhere. Work up to starting it and sitting in the drive then ease into short trips. Use toys, treats &/or verbal praise and lots of petting to reward them.
It's also important for you to remain calm and not anticipate their anxiety.