I have a 6X12 run that's built on a slight down hill slope (4" in 12' ). I have a couregated roof with 1' overhangs on each side and the sides are all open. I currently have a dirt base but am leaning towards adding 4"-6" of sand or a gravel base with a sand topping, to aid the drainage issue. Living in Reno,NV., The sand is going to get wet in the winter and possibly freeze solid. I'll wrap the run in plastic during the winter to keep it as dry as I can. Is the sand idea a good one or should I try something else. I'm open for suggestions.