Not all Roof Racks are OK for a Roof Top Tent. It's crucial that a Roof Top Tent is securely mounted. Required Roof Racks need to be:
Gutter Mount
Track Mount
Fixpoint Mount
Flush Rail Mount
Raised Rail Mount
Or a Roof Tray
Clamp Mounted Roof Racks that secure the rack in the door (for vehicles with normal roof) are not suitable for Roof Top Tents.