ok, not trying to get into a argument here, and I agree that indoors is the way to store a machine, but there is moisture in the air at all times. Homes are sometimes even worse than outdoors with central heat and air etc.
Most of the machine I referenced that had rusted fabric were stored indoors.
You have the freedom to do as you will, but I am trying to give advice to folks who may not have all of the knowledge and or experience to make a call like that. Not everyone has dealt with a couple hundred antique sewing machines.