Keep the strings on, but tune them down a bit.
Personally, I would keep them in the case, lying down. This is purely to protect them from getting knocked over, which might be a possiblity with the other options you mention.
You don't mention how long, but get some of those little silica packets as well, and place them in the cases to keep out the moisture. Although this might depend on how humid the storage place would be.
Personally, I would keep them in the case, lying down. This is purely to protect them from getting knocked over, which might be a possiblity with the other options you mention.
You don't mention how long, but get some of those little silica packets as well, and place them in the cases to keep out the moisture. Although this might depend on how humid the storage place would be.