Which kind of crossbar should I use for the LOFT?

You will need crossbars on your rack. Some vehicle racks come with them; otherwise, you'll need to purchase crossbars and "feet" to mount them to your specific vehicle. We sell Thule products, and you can figure out which ones fit your car by using their guide: https://www2.thule.com/en-us/fit-my-car
The LOFT attaches to the crossbars with included hardware.