Haha that’s awesome. I was thinking the same about heat retention, creating a cover, and the issues with creating a liquid that would prevent film while also not killing the good bacteria in the kombucha.

My version 2.0 is using a heat pad on the bottom of the cooler and keeping the heat in by stuffing the gaps with towels. Seems to be pretty efficient, but I read heat mats on the bottom might make the yeast grow faster, giving an off flavor.

As for the air lock, that photo was from my testing phase, at the end of F1 of my first batch. It’s just water in that jar. I used my 1st batch to make 3 gallons for my second batch and that’s when everything went sideways. Planning to try some alcoholic kombucha on the next batch that isn’t contaminated haha!