I just built the box out of free wood a couple of weeks ago (I had a lot of material and a couple of weeks off). I currently have the top covered with plastic to keep it dry until spring. I am thinking that I will use a marine grade varnish on the exterior once things warm up. OSB was not my material of choice, but it beats hauling everything back and forth all winter through the snow (before I built this, all my brewing gear was in a shed at the corner of the lot. If I have to rebuild it in the spring I may just build the whole thing out of concrete board and tile it.