Most of the collapsible dog crates are fin efor in the car, but it might be best that the crate you buy has two door (some only have one). that way if you are in an accident and one door is blocked, you have an alternative way of releasing the dog.
I would also reocmmend that you do not get one too big for the dog. Yes you want to give the dog ample space, but a crate that is too big can result in the dog being thrown agaisnt the side of the crate in an accident, causing nasty injuries.
There is also a more expensive option, and that is to have a custome made crate built. This woyuld make the most of any available space in your car, where a normal crate may waste some space.
You could also have a tialgate and grille(guard) as opposed to a full crate if you are sure oyur dog would not be destructive.