If they remain dry they will be fine.
If you have dirt floor it would be a good idea to keep them from touching the ground as dampness can creep up and possible freeze.
Wood pallets are everywhere for free. Scoop up one or two of those if you have a lot of stuff to store.
Some pallets will fit in a car trunk.

Thanks for the information tufaenough, especially about the tip on the dirt floor. I've got a couple dozen (so far) to store for a plant sale next June. I've really enjoyed making these things and appreciate all the help I've received from the GardenWebbers. What a great bunch of people.

You are welcome Fleur.
That is quite a few leaves.
The great thing about pallets is if you do get frost heaves they will lift everything together because they are ridgid.
If you use plastic or even a sheet of plywood the ground frost can lift in some places causing your leaves to possibly rub with the movement.