I can't help you, but I am also interested about this topic. What type, model, and thickness of insulation do you have now. I have a Casa90 and will be pouring the hearth next week. I was thinking about getting an extra 2" of FB board for the bottom and adding an extra 2" of blanket. I would assume that if the insulation is good I could add some preheated fire bricks for thermal mass to extend the desired low temp cook for 18 hours (225 to 270). It probably would not be hard to calculate based on ambient to make it work.