Another idea just came to me.
Machine the frame accurately in steel, ali, or low grade stainless, and then e-coat it.
E-coating (aka electrophoretic paint) produces a very uniform paint finish, usually around 20Ám thick.
It is good for 1000+ hours salt spray, so you'd be safe on the corrosion front.
IDK what it would do to the emulsion though.
The process is widely used by the automotive industry, so it's easily availlable. Plants are often willing to run small batches of products through between major runs, as the paint stagnates if it is not kept moving.
I guess it's an option worth checking out.
there is a bit more info here: (scroll down to electrophoresis) http://www.alu-info.dk/Html/alulib/modul/A00344.htm