No need to cover fermented feed unless you have a problem with flies/pests, in that case some cheesecloth works well.
When starting out with fermented feed, do NOT make a large amount of it - it can take them days or weeks to catch on to eating it, so you don't want to waste pounds of feed by over committing.
I do a very simplified, dumbed down version of fermented feed: 1 large jar, add dry feed, mix in enough water to cover by about an inch or so (actual amount of water needed varies based on feed and weather conditions), and then I start serving it the next day. Once I run low, I just dump in more feed, more water, and continue from there. I only wash out the jar if it gets pretty gross and crusty.