For most people you would assume high temperature resistance would be preferable. I imagine most ways that people store this won't be at risk of coming into contact with corrosive substances. However, a house fire is much more likely. House fires might not be enough, but I guess it depends on the specific circumstances of how its stored. For example, storing your backup in your garage which has a ton of fuel around could increase the risk.

I will say one thing though that its time to put on your tin foil hats. Don't store your washers in your kitchen cupboard that has anything with chlorine in it . Chlorine will eat away at your stainless steel as its particularly vulnerable to it. It's worth mentioning that your tap water could potentially have low levels of chlorine in it, so if you have a pipe that could be dripping onto them for a while, obviously depending on how you store them, over time you might have a issue. Though, drinking water is usually has a very low concentration of cl2. Although, some places might be more than others. 1-2 parts per million could potentially give you that corrosion over time, and that's obviously ignoring the damage the water could do itself.