Well I have a solution - not finished, I messed up the bend. 1/2 EMT conduit. I have the bender already, 1/2 is cheaper than dirt, and there are plenty of fittings available that can be used to secure it.
It's reasonably strong, corrosion resistant, smooth (no cuts), lightweight, and if I wanted to I could even run a wire through it and hook up a high mounted taillight.
I'll post up when I have a finished product.