I used to use the large ones for lurcher kennels , drill a hole half way up the lid then use a jigsaw cut a straight line across the center of the lid and then cut a semi circle opening , that’s enough to let the dog in and out yet stops the bedding falling out .
drill hole top and bottom of the barrel then you can attach couple bits of wood to stop barrel rolling and get it off the floor , I used straw as bedding .
not as fancy as the metal doors or sunbathing platform etc but lot cheaper.