You can store a Model M or Model F pretty much any way you want. They’re built like tanks. For best results though, don’t store it with the keys held down (i.e. don’t just make a stack of 20 loose keyboards on a shelf), and protect it from dust with some kind of cover or container. If there are ABS parts (e.g. the case on a Model M), keep it out of direct sunlight. Any kind of box would be fine.