Thanks for the worries. The wood is not stained or sealed, the tubs do have holes melted into them every 2 inches or so with a soldering iron. I live in Houston where the relative humidity INDOORS is already pretty high and since I used a hardwood (birch) the likeliness that it would warp just sitting there here in my AC'ed living room (73ish degrees) is highly unlikely. The flexxwatt is doing a good job keeping the tubs warm on the one side. Amazing how such a thin and basic material can get that warm!