Hi folks. I've been pondering a cheap way to make a couple of rain tarps. Steep & Cheap has some tent footprints for 4 person tents pretty cheap. I'm thinking about picking a couple up and modifying the shape a bit to fit my needs. What are your thoughts on the materials used on tent footprints? Suitable for a rain fly? The material listed is 70D Nylon, 1800 mm.