The box was a manger from the barn (28x28 inches), I used 2x4 to make the bottom. A 1 inch O.D. pipe for the tuyere, a slab of stone on the bottom with the two firebricks to make the back wall of the firepot.
I filled the corners of the box with lava rock in hopes that I could shave some weight from it and keep it mobile. I'm sure it helped but it's still hefty!
There was some coal in the basement, probably 50 pounds total, I used maybe 5 or 6. A bit of cardboard and paper some sticks, and used my compressor to push air. Once the fire was going good I added the coal.
Had to play with the air flow, but it made 1/4 inch metal glow and I got to practice straightening/bending a little!
Thanks JHCC for the advice about the lava rock!
And thanks to all the people who have posted their designs, diagrams, thoughts, and their problems. Those who posted their problems kept me from the same!
Please feel free to correct any issues you see!