If you don't use a sheet goods or a 1x solid cover deck with a good water proof membrane under the steel roofing it will rain inside as the steam that hits the cold under side of the roofing condenses. Trust me, every drip finds the back of your neck. Either that or use a hood over the pans.
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.