A few ideas.
I'd try to go with a 500 gallon plastic tank. Having 5 times the capacity it'll take longer to freeze, especially if you insulate and enclose it. I'd insulate the pipe and if possible shovel dirt over top of it. Since you can gravity feed and the tank is spring fed you might be able to let it drip during cold weather. As long as you can keep some water moving it shouldn't freeze as easily.
"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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