
I bought this for a long family trip from New York to Quebec for the waterproof keeper. I think this point is imperative. Although I have never used a car lid without this mat underneath, I can tell you that this item keeps the car lid in place. Without them, the bag will move unless you attach the topper as tightly as possible. This rug really held the topper in place. It works. Just lay it on the roof, put the car topper on it, load it up, lash it down and nothing will move.

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