There's one lake we camp at that is terrible with flies. This time of year they get thick and even thicker into the Thanksgiving weekend. You can end up with 3 dozen flies in the trailer! How do you keep the flies a bay? I use a box fan inside blowing at the door and one outside blowing at an angle away from the door. We'll end up with about 12 instead of 36. Fly tape, fly bags, fly spray don't work on these guys. They're thick.