OK, one of the few schedules I remember, 4" (4.5" OD) sch 40 is 0.237" wall and sch 80 is 0.337", so, that's close enough for them to call it 3/8".
I measured it this morning and it is very close to 3/8" so that's what I'm going with. The size we'll be using for the feed rail pipe is 2-7/8" and I believe it sleeves right inside the larger 3-1/2" stuff. We thought about doubling them up on the corners but 3/4" of steel seemed excessive
My British friend always said "Don't worry about culture, Andy, you get it in yogurt". However, the comment I was making is if you get a 6 ft fill in place and it sets for a couple of years it will settle and compact more on it's own, which will help you in the long run. Ten years is better.

But it is really hard to properly compact 6 ft of fill.
When the dirt work guy put the chicken barn pad together there was almost 11' of fill at the North end. He made a point of driving to the North with every pan full of dirt to mash it all together. They did some compaction test every few feet and it always passed so it must have worked. I'll most likely hire that dirt work out so it goes quickly and smoothly done by guys who actually know what they're doing. My Grandpa always said a good rule of thumb is 1yr per foot of fill to let it settle if you're not going to pack it. I'm 100% sure there is no science behind that but it sounds good.
Of course knowing the carbon was sequestered in the wood would lead some people to claim it is better left to rot than burn. For those people I have a technique they should like. Carbon gets sequestered in a landfill, and paper companies have a marvelous carbon collection machine running to grow millions of trees to make paper. When you save a piece of paper you don't "save a tree", you keep a tree from being planted.

So at work, if I needed to print, I printed 11 copies and threw ten in the trash to be safely sequestered in a landfill.

Then the paper company will plant more trees and take more carbon out of the atmosphere!

You are truly ahead of your time. I print one page and bring the other 10 home to start the fire in my stove that is burning all my scrap lumber
I'm green.
There have been a few times I've been able to politely inform the naysayers that an acre of corn removed 8 tons of carbon and puts enough oxygen back into the atmosphere to supply 130 people with oxygen for a year.