I had exactly the same questions when I was thinking how to make the cover. So this is how it is covered in stages:
As you can see there is a lot of space that has no mulch under the tarp, so I hoped it will provide micro-climate under the tarp. I mulched in case my protection will not be enough to at least keep the roots and graft alive. This is my first year with it, and I am jumping a zone, so trying to be proactive. 