I have a newborn baby who is 3 weeks old in the backseat. A large dog crate won't fit in the backseat and I don't want to leave him loose in the backseat with the baby unsupervised. So far he's been very gentle but its too distracting to drive and watch him. Plus he gets dog fur all over the baby seat.
I have a Lexus GS430.
Someone that comes to dog park uses one of those trailers for his two huskies who seem very happy to travel in them.
They are 5-6 feet back from the vehicle's bumper and have a deflector in front so your dogs don't breathe in exhaust fumes.
I was told that they are very popular with owners of sled dogs and hunting dogs who take to the trailers the same way they take to their own crates at home.
P.S. Pics of baby:
http://members.shaw.ca/natasha_pannu