If buried in snow, it should be OK for a day, maybe 2. I would not try for longer. At 8% you would want 30F to hold longer and depending on the temperature in the tank you might get 35+. Realize that one essential on cooling is the mixing to have a uniform temperature and that will not happen in the tank you describe. Secondly, plastic will not transfer the cold well to the concentrate.
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.