I built a 5' x 12' wood shed with MasterRib metal roofing on a 30 degree slope. This is the first winter I have had it, and today a foot of snow slid off it all at once. My small kids like to play around it, so I'd like to err on the side of safety and put some sort of snow guards on. Are the Gutter Supply no. 100 stainless snow guards the best bet? The plastic options seem flimsy. How many would I need? Is 18" spacing close enough for this application? The installation instructions seem to say 15" spacing with multiple rows, but that seems like overkill for the shed.