There are a lot of cheap roof bags, which sit on the car roof. This can cause scratching and they are not secure, fitting just with straps. The reason the Maypole bag is a premiuim product and beats more others is because it has steel runners to give a solid base and bolts securely to the roof rails.
320L Roof Bag
The easy to store alternative than a roof box
Protects load with waterproof material, seams and sealed zip
Fast and secure fitting with a solid base
Universal fitment - Fits direcrly onto roof bars (min 66cm/max 82cm roof bar spacing)
High tensile U bolts
Max capacity 50Kg