A second thought I've had is if anyone has tried a tarp door that doesn't split (a third wall more than a door). My idea is that when you locate your tarp you will usually have the wind from one dominant direction. By placing the door on the side getting the wind first it is assumed you would naturally only use the other opening anyway, so the split is unnecessary. It would also likely be easier to design, and would need no connector at the door split bottom.
Has this been tried?
“The word 'hammockable' (describing two trees that are the perfect distance apart between which a hammock can be hung) is not in the dictionary, but it should be.”
― Dan Kieran, The Book of Idle Pleasures