To answer the question on the vinyl flaps on the inside, I looked at a newer model (Mine is a 1990) and they look alot more secure than mine. The flap actually folded around the lip with velcro the entire lenght of the flap. Mine lays up to the lip and has several velcro flaps along the length. I measured the gap when it was set up and cut several pieces of sturdy styrofoam and place them in the gap after it is set up-takes about 1 minute to do both sides. Haven't had a problem since then