I normally put our out of season clothes in one of the bags you can get the air out of and then put the bad into the suitcase and store them in the attic.100+ degrees in the summer and -10 degrees in the winter (in the attic that is)

ten suitcases? That's a lot! (though maybe I have about that many now--not all hard, though; we have one hard suitcase for each family member, no more)

I store my suitcases in two places.

My own suitcase (w/ smaller totes/soft-sided suitcases inside) sits in the back/bottom of my closet.

The others go up above a tall (9' ceilings), deep closet we have.

If you truly need 10 (if I read that right), can you switch some of them to being soft-sided? And then they can go inside the hard-sided ones, which might take you down to 4 or 5 needing a space?

I don't know about the temps for suitcases; I don't think they'd melt at 110 degrees, but the heat might shorten their lives. If you're willing to pay that price in order to find a place to store them, that's a bargain I'd understand. (My suitcases fly regularly, which means they get sort of banged up anyway, so losing a few years off the tail end of the livespan really doesn't worry me.

(Installing fans and insulation to cool your garage would make it a more attractive storage space for lots of stuff, but that's sort of a major undertaking)

Do you have a basement? We store our suitcases one inside the other (half are soft, half are more structured though not totally hard shelled) near our washer and dryer. They're on a low shelf to keep them up off the floor as we sometimes get some water in the basement.

When I lived in an apartment I stored my suitcases (I had a grand total of 2 at the time) under my bed.