If I were a medieval King, I would store my gold in a stone chamber beneath a foundry, gold would be stored by melting the gold down and just splashing it into the chamber so that the hoard would not be individual coins but a giant pile of glorious frozen gold, making it impossible to steal easily. In the event liquidity was required, we would cleave the gold with dull axes, but long term cold storage would be glorious Stalagmites of frozen gold.