I was searching for this type of roof carry bag for almost a year. Best part is that it can be put direct on car roof. I used it for my trip to Goa, just lay down bag on car roof & load the bag with luggage, zip the bag & strapped to the car inside. Was scared as bag will fall off even though strapped tighten, unbelievable at 120km the roof bag stayed safe. Non slip mat not required as mentioned must have one below. Inside this roof car bag I had put in 3 mid size suitcases, 4 gym bags & 1 large suitcase. All stayed secured through out both ways of the journey.