Hm I thought it would have been 7.5”x7.5” square for an 8” round and mine is inverse of that.
Yeah it is the snorkel tub. I picked it up second hand tub preassembled stove not installed. They never put the stove in because the tub never sealed and first time I heated it, it stopped leaking.
The pattern I just made up on that graph paper and then changed a little so the narrow edge on both sides of the riser would be more connected.
I might use ss screws or wire pins to hold it a bit. I’ll put some earth/sand mortar in the seams before I put it together and place it in its aluminum box.
Right that’s about what I was thinking I guess it doesn’t need to be pretty, just trying to make the core as relocatable as possible.