I don't wish to rain on your parade, daveycrocket, but do you have all of this in writing yet? The cargo net retrofit involves removing the headliner and cutting holes in it where the mounting points go -- two right behind the front seats and two above the cargo cover area. It is great that BMW and your dealer have agreed to do this, but I find it remarkable that they would do all that work for $138. I would get a clarification on what they are going to do and the exact scope of the work before proceeding.
Good luck with the retrofit. I agree that the cargo cover is not explained at all well by BMW. Others have gotten dinged by this, too.