Shango will howl very, very loudly if I put him in a small carrier. On short trips, he never stopped and on long trips he would stop for 30 minutes or so, but then he'd start right back up again and continuing howling off & on the entire trip. I ended up getting the Sturdi double car go carrier with a hammock inside and he is now the best travel companion I could ask for. He naps in his hammock pretty much the entire way whether it's a 5 minute drive or a 5+ hour drive. On long trips I keep a litter box on the floorboard and let him out occasionally, but to this day he has never used his litter box in the car. He always holds it until we've arrived at our destination.... I still put in in there since I figured the one time I don't is when he will actually decide to go potty while in the car. He also refuses to eat/drink while traveling... but he does make a mess splashing water all over my car when offered to him. I highly recommend getting a very large carrier like the sturdi double car-go carrier. It's made traveling with Shango 100% better. The last long trip he went on with me was about 10 hours of driving and he only whined/howled once because he wanted out to sit on my lap and get petted for about 20-30 minutes, then he actually got back in his carrier on his own and went back to sleep.
You might also look into felaway spray and spray some inside his carrier to help make the trip less stressful. I personally haven't tried it yet, but plan to the next time I take Shango to the vet.