This is a great article. I haven't had any issues with the zinc and rebar but I have also never heard of putting a dowel into the bottom channel of the came that is awesome. Would that same principle work by filling the bottom of the channel with caulk or the like possibly giving the window space to spread in the seasons (I am in Chicago and the weather is so varied that a door which closes nicely in the winter has to be given a shoulder and body weight to close in the summer because the wood swells so badly. I see more actual outward bowing than downward slumping in panels here.