There used to be a barn painter in Pennsylvania who used an old fire truck with a platform wide enough for two or three men to work together.  His technique was for one or two men to work sprayers and an additional man with a long handled brush  following them and brushing the paint.  It wasn't just the seams; they brushed every part of the surface.  It really did seem to help, and his paint lasted a good long while.  For what it's worth, he was firmly committed to using Athey paints.  He also did roofs, which was fun to watch.  They ran the hoses over the peak and used them for holding the men.  They never used ropes or harnesses; just walked down to the edge of the roof and someone would pull the hose back as they walked backwards up the slope spraying as they went.  Get to the top and walk down to the edge and do it all over again.