Hi summertime,
We purchased a 36" crate for Roxy shortly before we collected her. However our breeder advised us that actually a 30" crate is better and just as good as when it comes to toilet training they aren't as likely to mess in the place they want to sleep in. We stuck with our 36" crate and TBH she was fine, not a lot of accidents at all. Admitedly we cannot fit it in the back of our car (well it fits at an angle but not very useful

) but she has a harness for travelling in.
She uses her crate all the time and it's a great little retreat for her especially if we have children over. If she gets fed up or tired she takes herself off to her crate where they cannot get to her. They really are a useful bit of kit!
By the sounds of this you want to put it in your car so a 30" crate will probably suit you best.
