Weatherproofing is simple….Order a suitable screw lid box from the likes of RS Spares or Maplin drill a hole in the centre of the base large enough for the spindle and place it between the back of the clock and the movement (ensuring the movement you order has a long enough spindle). Once assembled screw the lid on.
If you are still worried about water ingress, add silicone sealant between components and lightly coat the mechanisim spindle with molybdenum or lithium grease…….that should do the trick