Rain cover

My idea is for a cover that will slide out over the opening of the rear door in van's and suv's to alow for "dry loading of children and groceries. We all have had that time when we are putting in the carseat, buckling up children and loading the 20 bags of groceries in a rain storm. Why not have a cover that will come out when the door is open? This could be incorporated in the power open or have it be a manual cover that will pull out easily with one hand.