Good to hear it all worked out. You will find crypts with upto 4 or 5 times that amount of iron. In my experience, the smaller the swamp biome the more rewarding the few Sunken Crypts can be! I am working a small swamp biome attached to the Plains where Yagluth's altar is. It has only 3 Sunken Crypts and it has 3 Abomination spawn points. I have probably close to 200 tame lox on the island, some having moved into the swamps. Every couple of game days they help me get 15 Root. I already have enough to make Root Armour for all 3 of us.