Neat! I can't wait to see it in real life
The mast reminds me of our 2007 robot, which had a round mast in roughly the same location. We attached a block on the belly pan that fit inside the bottom of the tube and then cut a hole in a sheet of aluminum that was then attached to the frame across the top.
http://www.photos.project1726.org/al...0/IMG_1681.JPG