The case of the disappearing lens cover

[Elderdude]

While camping near Santa Cruz last week, we noticed one of the light fixtures under the roof vent was missing it's lens cover. We couldn't find it anywhere inside the trailer. We needed another item, so we bought a replacement cover at the same time at a trailer supply shop. When we popped the trailer open back at home in Sacramento, the lens cover was missing again! Once again we could not find it anywhere inside the trailer. Today my wife found both the old and new covers on the grass under the rear of the trailer. How did both get dislodged and where were they hiding?