If you are watering growing plants in a greenhouse, I think that the hot air at the top of the greenhouse will be humid. The way I see it, this consistently warm air going by your wood, if it is moist air, is not going to dry your wood. You wood is seeking equilibrium with the air in regards to humidity. Dry air will dry wood, wet air wont. Or is this just a greenhouse type of a structure, but not used for growing plants?
If we then put the wood inside, and then a wooden top to form a seat - if we pull in the heat from the top of the greenhouse to the bottom of the box with venting tube as a fan, it should help heat the wood, and also super dry it - a wood drier is another thing on our to-do list!
All of the world's problems can be solved in a garden - Geoff Lawton. Tiny ad:
Getting ready for the Better World Book kickstarter - February 2019https://permies.com/t/99513/ready-World-Book-kickstarter-February