Most Heatsinks are made of Aluminum.
Copper Heatsinks are BETTER, But Rare and EXPENSIVE.
Stainless Steel is Not a very good conductor of heat, so its not very useful as a heatsink. I Doubt anyone makes them.
Its Not practical to put an Aluminum or copper Heatsink INSIDE your Cell.
The KOH will eat it away.
On the Outside is Good, Especially on the Sides.
Bottom, not so good as Heat Rises.
A Good Heatsink is Extruded metal, All one piece without any joins.
So making them out of pieces of metal bolted together is not as efficient.
But YES, Your other suggestions are practical and will help to keep it Cooler.
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