The pelter coolers I have are rated for around 450 F maximum if I am remembering correctly. Realistically the information I have found relating to typical pelter coolers is what ever the melting point of the solder is that holds the junctions in place is what will determine the top thermal limit.
The way they work is the greater the temperature difference across them the higher the electrical output.
The old style pelter devices were far less efficient than what they are now. Not outstanding as power generators but still they do work well enough in conditions that are within typical persons ranges.
I had played around with mounting mine on all sorts of different things. The boiler stack was the only thing I had that was under the top limit but yet had open air flow to keep the cool side heat sink temperature down.
With a little cooker unit I think that if the cold side heat sink was made out of square or rectangular tubing so the pelter units had a flat surface to attach to water could be circulated through it and aid in increasing the heat transfer effects considerably.
Then just use a small radiator or what ever to dissipate the heat from that.
If I ever get my shop concrete poured it will have the in floor heat tubes And I have been pondering on how to use a bunch of pelter units in between the boiler supply and the floor coils. Concrete floor heat doesn't need the full 200 F boiler water and will take 100F just fine. Given a 100 F drop across a good number of pelter units I should be able to get a reasonable amount of electrical power that way.
Even if I only get 2% of 200K BTU that gets transfered to the floor coils turned into electricity that is still nearly 1 KW of usable power! Take that times 12 hours a day for 5 months and thats a good deal of free power!
In theory of course! cost of set up may determine the actual out come.