This is what I do. I just place it in a plastic bag and don't use it for about a week. I have enough to let me use one each day and quarantine the used mask for a week.

What's the plastic bag for? Seems like a good way to promote bacterial and fungal growth.

I'm using open plastic bags for avoiding touching the mask itself. I figure there's enough air circulation when I let the bag sit open on a shelf. Granted a paper bag could be better.