Emily, we don't have a car that can fit 4 bikes inside that gets the gas mileage you want... DH has an SUV (the kind people here make fun of) that easily fits 2 bikes with the wheels ON, but we have a Saris rack that has an extender for 4 bikes, that we use for trips with our friends. We just use a huge cable lock to keep the bikes safe. I've never worried, really. Once we get to our destination, the bikes are stored somewhere.
I know I must be spending too much time here. I just told DH, "My friend in Belize is moving back here."
I've never met you in person.