1. Proper Al alloy, hard anodized.
2. Paint on top of anodization.
3. Lay up outer layer with s-glass or basalt plus barrier coat of epoxy on mast tenon that goes into fuselage. Same for wing attachment areas.
4. Good barrier coat of epoxy and/or paint on wings too.
5. Carbon fuselage not such a bad idea.
A hybrid stainless steel and carbon fuselage also interesting.
Or hollow, forged and welded, or 3-d printed, stainless or titanium $$$$$$$$$
Carbon just makes sense, but still $$$
Could one do a hollow titanium tube version of Levitaz stainless rod?