I ran AUF on my last evaporator by entering from the rear down low. I plumbed it into a 4" heavy gauge round duct. It reached in all but 4" from the front, and there I capped it. I had 3 rows of holes, one top center and one on each side facing the outer grates. Each row was 5/16" about every 2.5-3", but mine was on a high pressure blower. If you are going to use a squirrel cage blower, the same idea will work, but I think you will want the holes larger. Try 3/8" and see how it does, if more air is needed drill the holes 1/8" larger and see if more is needed. Repeat until you find the right size.
While I had a high pressure blower, most will use a squirrel cage blower.
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.