I've never found anything that stops water from freezing when it's minus several degrees outside, even in an insulated shed. Insulation will stop the temperature dropping to a certain degree and will keep the frost off but it can't stop the ambient temperature from nearing the same as the outside temperature if there's no heatsource from within. I've tried heating bricks to stand bowls on, snugglesafes, surrounding a bowl with a deep layer of straw etc etc. That's why I installed tubular greenhouse heaters in both my sheds as I was worried that the buns had no access to water for the 8-9 hours I was out at work, never mind during the night. Hope you manage to find something that works for you.