I've recently been doing a fair amount of MN winter camping with my trusty MJ tarp, which I love...but last weekend it was SUPER windy and although my MJ held strong, I've decided I want a tarp with doors for added protection from the cold winter wind. I know you can order a door kit for the MJ, but I think I want to invest in the Superfly. What is the difference between poly and nylon? My Mamajamba is silnylon and I like it a lot - just wasn't sure which material to order the Superfly in...