Many years ago, I made some honey supers with side panels that were made of waterproof plywood that was skinned on both faces with "Formica laminate". This material was very strong and was available at the time at zero cost.
When these boxes were in use, a slight problem arose in that the Formica faced parts did not expand or contract with variations in moisture content, but the natural wood parts did. The result was that in wet weather (very common in UK) narrow gaps would open up between supers of this type and the 1 mm slots would admit a small amount of rain.
This was also at the time that I first introduced the non overlapping insulated roof and I was concerned that this may also be a source of more water ingress. So I decided that I would place drain holes in strategic places so that any water that did get in (for whatever reason) could drain away regardless of any tilt that was deliberate or accidental.
I first tried groups of three holes, each 2.5 mm in diameter, spaced 10 mm apart in the rear corners of the floors... My reasoning was that a single hole may be blocked by a leaf but a group would retain some degree of porosity. When in use this method was not very successful as the holes were small and rough fibres inside the drilling would expand with moisture causing particles of dirt to lodge in the holes and ultimately block them.
I increased the number of holes to four and increased the diameter of each hole to 3 mm. This system did not block and I now automatically put this set of holes, using a drilling jig, in every place where water could collect on a horizontal surface. I do this on every piece of new equipment that I make and any S/H parts that come my way.
Several years later I noticed some hives where water had collected in the space under the frame lugs and I resolved to sort this out. This was achieved by diagonally drilling 3 mm holes from the corners of the recess downwards and outwards so that any water in any lugspace would drain outside the hive body through one hole or the other, no matter which way the hive may be leaning.
When I first thought about drilling these holes I was concerned that the bees would defeat my object by propolising the holes. I was wrong, this has not occurred, the only blockages have been from swollen wood fibres or the occasional wax moth grub crawls into a hole and spins its cocoon. A run through with a 3 mm drill bit in a battery powered drill sorts this out!
From time to time my equipment is returned to my workshop for scrubbing, flaming and an application of linseed oil as well as petroleum jelly where needed. At this time I run a 3 mm drill through each of the four holes which clears out any fibres that have swollen with damp.