A hamster travelling in a car needs to be in a pet carrier - something like this guinea pig sized one. Big enough to put a small house and plenty of soft substrate. And it needs to be wedged in (or held on someone's knee) so it can't move about. If you had to brake suddenly the carrier could be thrown and injure the hamster.
https://www.amazon.co.uk/Ferplast-Al...rplast+aladino
So a cage, even a small one, isn't good for car travel as it's dangerous for the hamster. If they're in a cage and you brake suddenly everthing can crash onto them or them be hurled against the bars. A pet carrier is cosier and safer for them.
You can take a smaller cage with you to set up when you get there though. They can be ok in a smaller cage for a while when on holiday. But if you're only going for four days I wouldn't take the hamster - too much stress and change. You'd be better leaving them at home and have someone come in daily to check and feed them.
I would only take a hamster on holiday if the journey isn't too long and you're going for a week or more and staying in a place where you can set a cage up and leave it in the same place for the duration.