At the Tulare Ag Expo, I asked about working in trees.  One of the Trimble Techs said that a Trimble 5xx construction receiver was very sensitive and often worked indoors, and might work in trees.  In a metal building with reflecting surfaces?  That was not discussed.  Sorry about the 5xx, but I was not paying close attention to that.  This receiver used a wireless data link and I did not see a way for it to work for me.