I guess I didn't include all of the specs in my summary, but they should be in the drawing. Interior volume is 600 cu in. My primary use will be forging my own tooling and knives. Don't see myself ever selling anything.
I came about my sizing this way: Started with ROUGHLY 5" HJ * 7" W * 12" L. I started here, thinking the 5*7 cross section is bigger than I need, but big enough to put stock in without banging on the lining too much. At this size, it's 420 cu. in. Too big for single burner. So I decided double burner, then worked sizing backwards. Keeping ROUGHLY the same cross sectional area, I started with 600 cu. in. (300 per burner). That's how I got my 16" Length. Then starting with mailbox shape, where W= 2*R and H=`1/2R. I used these ratios for two reasons: They seem reasonable, and they make the calculations simpler. That's where I derived all of my interior dimensions. Exterior, I added 2" in each direction, and rounded up a bit to account for the hard liner.
I was planning to use ITC-100 as a liner over the wool blanket, followed by a kiln wash, not yet mentioned. Haven't found an available source for Plistix 900, still looking for Matrikote. I'm looking at needing 1 pint of ITC-100, so $25 isn't a deal breaker. I was also looking at Kast O Lite 30. Might be cheaper per pound, but I don't need a 50 lb sack.
I was planning to aim the burners at about 1/3 of the way in from the edge, not the center of the floor. In looking at my own drawing, I can see why it looks that way. That line is used to indicate the penetration of the burner ports is not Top Dead Center, but offset to one side at about 10:15 (using clock angles).
Thanks for your input