This week I was reading about under floor entrances. I think this is a Dartington design, the main advantages been, reduces wind and rain getting in the hive, reduces robbing from bees and wasps. This inspired me to make some and see if they work. Its a very simple design and easy to make, much easier then a conventional floor. There is a short landing board with a vertical climb thought a 8-9mm gap, a mouse guard should not be needed with this small gap. I have made them from new wood, not overly expensive, the mesh flooring is still the most costly item. The landing board is made from recycled pallet wood.
If we have good results I will be making some to sell, so if any one is interested or have a comment, please drop me a line at firstname.lastname@example.org