Sourdough Pouch

Hi,  I been reading on wikipedia that optimal temperatures for sourdough are 25-30C,

however here in Canada we get that maybe a few days a year.  Few years ago was making sourdough, but since it was very cool the yeasts predominanted making it very sour, not very apetizing.  At warmer temperatures the sourdough would have a better flavour, also many beneficial bacteria grow at near body-temperature such as probiotics.

During the Alaskan Goldrush people used "sourdough pouches" alternately slung from neck or belt and typically made of leather.    I'm curious what modern (vegan) materials could be used to construct such a pouch, that would be resistant to the aciding environment, potentially HDPE.

Though I do have a food dehydrator, can probably use that for keeping a batch warm. I also have a leather belt pouch, and wouldn't mind having something like a sourdough pouch add-on.   Does anyone know how the original sourdough pouches looked like or were designed? a picture or blueprints would be nice,  I'm assuming they aren't sold, if they ever were, but if they are, I'd love a link.