Some are cast aluminum. In coastal climates the aluminum corrodes into a white oxide, leaving big pits.
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You are correct and a quick search after I posted it revealed that. I’ve just not seen aluminium used but it makes sense.
Stainless reacts poorly in heat transfer. Aluminum is gar superior in that physical characteristic. It would take a lot of amps to power a heating element inside a block of stainless steel vs. Aluminum at 150MPH in precipitation. Stainless also likes to twist and do weird things under heat.