I built my first greenhouse this year and wanted to do a double layer of poly so I can grow in the winter months. I haven't put the poly up yet but will be the next low wind day we have. My question is do I leave the second layer of poly on during the summer months or do I have to take it off? I have roll up sides and the one end wall will roll up as well to about 4' for all three sides. Any advice would be greatly appreciated.