Plastic gutter makes a good container for fermented feed. The benefits of fermenting depend on what you are fermenting, and what you are fermenting those ingredients with. How long it takes to ferment, and how long you can leave it out is highly dependent on your environment.
What your fermeted feed should look like when properly fermented depends on what you are fermenting, and how you are fermenting it.
I know those sound like non answers, but pickles are fermented. So is kimchi. Nato. Yogurt. Miso. Sourdough. Kombucha. Beer. Wine. Those products are not interchangeable. Fermenting "chicken feed" is much the same.