If you have access to soapstone then you can make a bowl out of it. Ceramic would work too. No heat stones, simply have a bed of coals which you will need to change out for new hot coals.
Here is a picture of a bowl I'm making which I intend on making sinew glue with. I imagine when prehistoric man did this it was a group effort in taking turns watching the fire and maintaing the proper temp. I GUESS anyways.
Heat stones in a wooden bowl and basket would work, but you would loose a lot of glue I think cleaning off the boiling rocks. Or you have a secondary vessel (holding the glue material) in the vessel which holds the boiled water like a double boiler. Again just a guess. So if you had Outbackbobs container you would make a smaller one and drop the heated stoned in the large container with a hide covering it all???