You can get a roll of Interwrap Roofing Felt on Amazon for $96. The felt should cover the entirety of your storage box's lid, with an additional five centimeters added to each side as a trim.

What if you need something now and don’t have the time to build a storage shed for your fire wood? You could get a firewood rack you can keep by the door, under a canopy. Or get a covered wood rack.