Will leaving an antique bed frame and mattress in a garage for a couple of nights damage them?

We had my brass bed frame in the garage for about 10 years, and there was no damage done to it. And it was not covered! I'm sure the mattress will be fine, too, with that length of time. People store things like this in storage containers or garages all the time. You might want to try using a dust mite cover, if you feel you want that extra protection. They're available at Target for about $25, and they keep dust and mites completely enclosed. This would give you that extra feeling that nothing could come of storing your mattresses there, if you still weren't feeling comfortable. Good luck!