Nit ure I can help. I have thule aero bars and change the feet depending on the car, with a roof box from Halfords. (Produced in the same factory as Thule boxes)
As we have two Golden Retreivers and a 6 foot son, for doggie holidays we have used the box to carry stuff we can’t put in the vack with the dogs.to be honest, I haven’t taken out any insurance for the box.