When I built my deck, the flooring was pried tight together and there is now a 3/8" gap between the boards.
You know, this got me thinking... (but thinking can be dangerous).
The planks are meant for flooring, so they have tongue-and-groove joints. There are three planks on top of each other in each sidewall (i.e. two joints between the planks). The planks in the front/rear walls are also meant to be horizontal (with the joints running horizontally). But: if I could turn the planks in the front/back walls by 90 degrees, so that they are vertical, so that they won't shrink in in the same direction as the sidewalls, then maybe the sidewall planks will shrink by "opening" at the tongue-and-groove joints instead of shrinking at the top and bottom of the hive box. If they shrink very badly, I may have to fill up some gaps, but regardless of how badly they shrink, the hive box won't become less tall because of the shrinkage. It does mean that I would have to use nails instead of screws to join the sidewalls to the front/rear walls. And I'm not sure if that means that I would have to use less glue on the sidewalls.