I did 6 - 4x4' for the side of our barn. I think one block is probably the best way to go. But I am not sure there is anything out there that will protect it from the elements. Mine were hung 3 1/2 years ago and all need to be taken
down and repainted. I didn't paint them onto the barn, I used Marine plywood, used a primer, painted with outdoor house paint then used a sealer, 2 or 3 coats . Good luck ! ! They really fun to do.