This setup won`t work with a single line retrac system. You need to tap into the gear up to close the door and the gear down side to open it. Maybe you could fabricate a spring setup on the door instead?? or use a seperate air tank with minimal to keep the door open and then the up side gear pressure will overtake it and close the door, the same seperate pressure would then bounce the door back open once the up pressure is blown off...ugh
V..