Some more pictures of the more-or-less finished product.
The clip toward the bottom is a quick-release for the mast, which is in two sections. Not clearly visible is the top, which is just a vertical 1/4- 20 UNC screw and a wing nut, like a standard tripod.
I may shorten the mast. I made it longer than I thought I would need because it’s easier to cut them than to stretch them.