Sand is not a good run medium. If you make it wet to avoid dust, it will freeze solid once temperatures start dropping. In addition to dusty, it also gets poopy and stays poopy unless you actually scoop regularly, because unlike carbon materials like plant matter (wood chips, dry leaves, grass, straw, hay, etc.) the inorganic sand will contribute nothing towards any composting action, so the poop will just sit there until you clean it. When it dries out, it gets pulverized when the chickens walk/scratch and grind it down with the sand. So now you have the chickens and yourself inhaling poop dust in addition to the sand/ash/dirt dust. Yuck.
I would highly recommend changing the medium to something plant-based that has larger particles, or at least a variety of particles. What I use is a combination of wood chips, dry leaves (which I collect in the fall, bag and store so I can use them throughout the year to add to the run), grass clippings in the summer, weeds from the garden, and any other yard waste I have. This provides a variety of particles which helps with drainage, and it keeps the medium from getting too dusty. It composts slowly over time as the chickens churn it. And best of all, you don't have to clean it! My run is covered on the sides in winter as well, and mostly covered on top, but I still have an open area at the back and some on top, to get fresh air in there and some moisture from rain/snow. So mine isn't 100% dry except immediately under the covered area. Having lots of fresh air in there and some moisture is good, don't seal it too tight.