Double wall baking pans

I have an old recipe for traditional German black bread (Westphalian pumpernickel), a 100% rye. It calls for baking at 160℃ (320℉), dropping to 120℃ (250℉) over 20-24 hours in a double walled baking pan, all the while keeping the pan filled with water.

Is this some sort of double boiler meant to keep the dough baking at 100℃ (212℉)?

Hamelman, for a similar bread, calls for  a Pullman loaf pan, and keeping a watchful eye on the oven temp as it drops over 12-16 hours. Have any of the denizens of TFL tried either method with "real" pumpernickel. Would a water bath suffice in lieu of the double wall pan?

thank you,

gary