Because our stones are on a mezzanine floor, and the French burrs extend under the upper floor, we had to build the tun so that it separates around its middle - otherwise we could never lift it clear of the stones. We built it from tongue and groove boards and never thought to fill the remaining groove at the bottom of the top half. It proved an excellent hidey hole for mill moth.
So, while we had it apart, we took the opportunity to put some wood filler in in the groove.