Oh Wow amazing, but wont they try to grow?
They won't want to grow until about May when the ground gets warm.
If I were to do that, they'd simply turn to mush in less than a week due to ground water seeping in the pit.
Yep! This is not an option if you have ground water. I have a good bed of gravel underneath about 30 inches of silt and clay. It doesn't have any water in it to a depth of 12 feet. I had to dig a test hole before I could get a permit to build. It was more about draining the septic tank, but the test hole was dry. I don't know for sure how close the water is, but deeper than 12 feet.
I had a gopher find my pit one year and he made a mess. Of course they have to try each tater, can't just eat one.
On storing onions in this dry climate, I dry them then put them in a mesh bag and hang them down the basement. They will keep until spring. You may have too much humidity for that to work there?
Gardening at 5000 feet elevation, zone 4/5 Northern Utah, Frost free from May 25 to September 8 +/-