A decade or two ago, I made one from some copper pipe, probably 8mm, though old enough that it might have been some antique Imperial size. A couple of supports, to bring it up to AA diameter, were made out of offcuts from uPVC double glazing. I don't think I bothered to tin the ends of the pipe, which would have made it a bit more corrosion resistant.
No photos, I'm afraid. I did hunt briefly, but it's probably buried in the depths of the bits box, superseded by alternator powered bike lighting, which isn't very relevant to OP.
