The end of September brought two vicious storms in the course of only 1 weekend, so the prospects of keeping the tarp up and the building site dry for the entire winter didn't look good.
But the hole in the top of the tarp seems so actually be helping! The wind now has a place to escape and building a frame completely around the edge of the tarp at least 4' off of the ground has both stabilized it and allowed the wind to exit. The trees on the edge of the building site have been strategically used to attach the frame which dramatically reduces tarp movement, the key to tarp longevity.
This tarp is 40' x 60' so it acts like a giant sail. Thankfully the masts in the photo have not taken to the skies as yet, although they do creak when a strong south-easterly blows in.
Another stabilizer seems to be the fish nets that we draped over the windiest side of the tarp. They give a bit but definitely help keep the tarp down in even the strongest wind (to date;).
It ain't pretty but so far, so dry for all the walls and the tunnel, which is all we hope for.