Assemblies for supporting a load relative to a roof of a vehicle, and vehicle roof tray assemblies are disclosed. Disclosed assemblies include an elongate member and an engaging mechanism. The elongate member defines a support surface for supporting the load, and has a pair of opposed, diverging retention surfaces extending away from the support surface. The engaging mechanism is configured to abut the retention surfaces to engage the elongate member. A slat for a vehicle roof tray is also disclosed.