If you are to get only one upgrade for your Corsair Arch and Smoke Stack, we would strongly recommend upgrading to stainless steel rather than the galvanized steel. This is because stainless steel is rust-resistant and has an indefinite life expectancy. The inside of a maple syrup evaporator is a corrosive environment. Every time you light a fire in a cold evaporator, condensation develops. The condensation will soak into the ceramic insulation and mix with the equally corrosive bi-products of wood-fire. This would eat through thin galvanized panels of a lesser arch within a few years.
Changing the arch from galvanized steel to stainless steel is NOT an easy change after the the arch has been built. This would be much more expensive and time intensive than it would be to start out with stainless steel from the beginning.
The mirror-finish stainless steel on your Corsair arch will match your evaporator pans.
Stainless steel is a food grade material.