Maybe my mom was right - I can't seem to leave well enough alone. My dislike of cast iron liners inside a firebox, and preference for high-temp ceramic materials, has been expressed often enough here, so I won't repeat it. The Nestor Martin X33 which I enjoy daily in the basement has all ceramic lining (mostly Skamol) except for one cast iron piece at the bottom rear of the firebox. I happened to notice yesterday that this piece is just wedged in place behind the side panels. So I took everything apart and removed it to examine it better. It's a 16"x9-1/4" piece of cast iron weighing about 17 lbs, and a half inch thick. Well, it just so happens that the Zircar RS-1200 refractory sheet that I bought last year for the Jotul F602 experiments is the same thickness, and I just happen to have a 16"x16" piece of it left over. What a coincidence. So I cut it to the right size (it weighs 5 lbs vs the iron's 17 lbs), drilled the holes for the side panel support brackets, and put it in. Perfect fit. Didn't have a chance to fire it up yesterday but I'll burn it today and report back. No temp measurements this time, just observations - I'm not expecting anything major.