Looks like you're running into some of the same problems Strat and Breacher had at "the Rock". Water and roads were always a problem, especially during the brutally cold winters.
In my area, if you go down 18" you wont have a problem with frozen water lines. Five feet would be a pia even in dirt.
On plastic tanks: You might look into one of the poly tanks specifcally made for water system. Our local Tractor Supply company keeps them in stock. Don't know about your A/O.
You also might look at engineer775's youtube channel. He specializes in off-grid water systems.
"The time for war has not yet come, but it will come and that soon, and when it does come, my advice is to draw the sword and throw away the scabbard." Gen. T.J. Jackson, March 1861
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