You can leave a car on jackstands for 40 years and it would be fine.

 

I stored my car in Colorado Springs - and mice LOVE to make a home in your exhaust system as it gets colder (if you don't drive your car frequently). Mice and rats typically don't like chewing through steel wool if they have a choice. They will typically avoid it - I imagine it's a little itchy. I surrounded the intake with it as well.
The result after three years: no mice, gerbils, rats, squirrels, bananas or dust bunnies. I consider that a success.
FTR - dust bunnies have been known to leap great distances - just check on top of your book case or kitchen cabinets. Amazing creatures.

 

I stuff my exhaust and intake with the same stuff every winter. As for the question about the jack stands, it is fine. I had mine up on jack stands while I had the wheels off for a month or so last winter. I took them off to clean them and then i was going to get them powdercoated, but I decided to save the money for something else and I got too lazy to put them on for a while. It is finw.

-Ian