I carry aluminum bikes on the back of my hanging rack all the time. Just drove 1500 miles with a 60# aluminum ebike. Velcro straps or lots of bungees to keep things moving together lessens impact on the bikes.

For some minor level of security I loop a cable lock around my receiver hitch than run that through the bikes with a padlock. Won't survive a night in a motel parking lot but good enough for restroom breaks and traffic lights.