Wood Rot in anchor Box?

OK update - I am getting there - I am ready to cut my wood block - I am using a Douglas fir 2x4 cut at about 8 inches in length. BUT how exact does the block need to fit into the V? Close enough or exact fit? I am hoping close enough since I am putting the 404 epoxy in the V behind the wood - so that should fill any gaps...am I right about that - or do I need to keep doing this to get this block to be a perfect fit..
 
From post #12: "Yes, Tony, I would shape the plywood to roughly the contour of the V. Then use thickened epoxy to take up any irregularities - that will help so you don't have to get that V-shape to be perfect."

;)