Crap weather so it's time to do some inventing. Trying to make this problem go away so no special tools or Rube Goldberg setup needed. Went and bought three different springs, took the unit apart to see where I could drill, how to attach the spring to the drain. Drilled the hole, ran a self tapping screw in the side of the unit at the top. Tried multiple positions of the spring, no joy. Too small to hold the spring to the drain wheel so got another ty-wrap and EUREKA! the weight of the large ty-wrap's clip and the length of it was enough weight, when positioned at the bottom, to keep the door closed. Problem was it was too long to sit on the bench. I need a substitute weight. Took a jacketed pistol bullet, drilled it small, clipped the ty-wrap short and pressed the bullet on the end. You can modify the install any way you like as long as you have weight at the 6 o'clock position. You may have to adjust the ty-wrap to get it at that point.
At least now when I see all that, I'll check to see it's closed. With the weight though, it's almost automatic.
https://photos.google.com/photo/AF1QipMCzJ_kaU3YncIkBURcWCk_MyOfp6Pu0XqM7IZO