Not sure they ever had salt on the undercarriage in the UK. 
Lots of dirt though.
Chiming in… The V&T had round staved redwood tanks, with square buildings around them. I asked one of the V&T historians if they used a heater of some sort, and/or insulation. He said no to both; the air gap was enough to keep the water from freezing.
This is a functional 2/3 scale replica at NV St RR Museum that they use for their steam locos.
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