Dear Caboose,
IMEX for a wet, salty environment, SS of an appropriate Grade is simply unbeatable. Any attached Workshop facility of reasonable quality should know the minimum requirements and be able to knock them up for you. The Grade is relevant unless you like brown spots everywhere.
Tried various cheaper homemade alternatives, all failed although protected mild steel is popular for equipment suppliers and generally seems to work for a reasonable lifetime. Maybe proprietary.
More friendly situations / cost tend to promote variations. Personally i would stick with SS.
Rgds / Charles.C
PS - i have audited flour mixing facilities put together with 2nd-hand equipment on a budget, mainly "mild steel". Some items look fine, some have had successive repaint jobs giving an ugly overall appearance. And similarly for the cabinets. 