I can describe it, but I have no pictures. My firebox (I have a 3x8) is 30" deep, a 2x6 will likely be 24" deep, The sides are bricked with full bricks as well as the back wall. My ramp goes upward at about 30-35 degrees, until it is up to 1/2-1/4" below the raised flues (that is the top of the bricks). Under the bricks on the ramp and the flat going back I have it filled with vermiculite insulation. To get that go to a greenhouse supply and buy BIG bags. A 2x6 may only need 1 bag. My 3x8 used most of 3 bags. I first priced it at Lowes and came up with $490, at a greenhouse supply I paid $60 total. When you calculate remember to account for the brick that will go on top.. Then about 6" before the back end of the pans there is a baffle that forms the back wall under the flues. Behind that it drops down to an enlarged chamber for under the base stack. Mine also has a clean-out door on the back to aid in cleaning the flues. I don't know if a 2x6 would have a rear door. In the clean-out chamber it is lined with fire brick, against the rear baffle, along the sides and on the floor.
I didn't, but since I put mine together many have started also using a layer of ceramic board or blanket between the sides and the brick for additional insulation.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.