I was able to form the aluminum bar for the curved parts of the structure around a straight coupling for rigid electrical conduit. The aluminum's springback left me with a good radius for the finished bends.
At this point I have the bar pieces pretty much in place. I have a few tweaks to add and a lot of clean up then I'll start adding sheet metal. Some I'll glue on, but most will be the back plates of the sub-panels which are held in place by screws. I'm planning on using the back plates as templates to hold the threaded spacers in place while I epoxy them to the frame work.