i have a simple chicken tractor for 6 chickens. im wanting to know during the winter time do i need to close the sliding door (that lets them out of the coop and into the run) during the night so it doesn't get too cold, an then open it again every morning to let them back out to the run. or can i just leave the door open all the time as i have all summer so they can go in and out as they pls. i live in central indiana so u have an idea of what the winters are her