The tube on an 8" dob is about 1200 mm I think, so measure your boot and see if there's enough room. Then you have the base, or mount to accomadate as well. Most people who move them about in cars tend to lie them (the tube) across the back seat with the mount in the boot.
I'm inclined to think that if it can be managed, you would be better off with an 8" dob than anything else, but I stress again - I'm not familiar with the Celestron that you mentioned.
Just wait a bit and see who else replies with what advice.
Take your time making up your mind as $5-700 isn't exactly chicken feed in any one's book. It's better to wait a bit and make an intelligent decision than to rush out and buy something that might not be suitable to your needs.
Ain't buying scopes FUN?
