Being both pans are flat bottom, pick which ever you choose, but make the draw off for syrup in the front pan. If you can arrange it, drawing from the front pan but at the back end for syrup draw works better.
I would think the 18x24 in back, then feed from that into one side of the 2x4 and draw off syrup on the other side.
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.