Here is another pic of the beginning of adding another layer of plywood on the back of the roof.
After cutting this piece, I test fit it, and put 4 gallons of water at the end of the 4' piece. You can see that the plywood does not conform very well to the layer underneath it. (red arrow).
That also is with the very edge of the plywood not fully flat with the edge of the lower layer. All I had on at this point were the plastic clamps on the edge, so adding steel clamps would buckle this part of the plywood up even a little more.
