Thanks for bringing up the single pull/double pull issue. Hadn't even thought that far. If it's a separating zipper, and the slider is single pull, it should be a simple matter to slide off the single pull slider, and slide on a double pull one.
Agree that a separating zip that is two way would be best, because it can be zipped from either end, so would make for a much more convenient door. Sleeping bag zippers are often two-way. That's why I was looking at them first, but could find nothing in #3 of that type.
Looked again at the T-H site, and their #3 6 foot separating zipper is not coil, but molded tooth, and zips only one-way. The Quest #3 is coil, but also zips only one way.
So will call Warmlite. If they are using #3 zips for their sleeping bags, at least I could get a two-way zip, even though it would probably be molded tooth. Will also check out Ragged Mountain nearby, but doubt they will have separating zips in #3 that are any longer than for a jacket. Should probably check out Joanne's Fabrics as well.
So the best case scenario would probably be a #3 molded tooth from Warmlite that is two-way for their bags, would be long enough for the whole door, but would be heavier with the molded tooth. Second best would be two four foot #3 separating coils from Quest, that would make the door removable, but zip only one-way.
Hate to chuck the whole idea just because of limitations on materials. That is getting to be a perennial problem. But a permanently installed door would allow use of #3 coil, which would be much lighter. Will call Warmlite first, before making a decision. Thanks.