Here is a closer view of the mount system I made to hold the 2" stainless tubing. Two ten-foot lengths of channel are spaced wide enough to hold a steel sleeve that is slid over the tubing. The sleeve is sliced and then two brackets are welded on and drilled/tapped so a bolt can be used to pinch the assembly. Opposite of this is the hinge which allows the birdhouse to be lowered for cleaning.  At the bottom is a short piece of pipe to which a bracket is welded and drilled. The lower piece holds the bottom of the tubing tightly to the mount in the vertical position. In the picture, five feet of the ten foot assembly is visible, the rest is buried with concrete at bottom and top of the hole.