I got married 5 years ago. I had mine preserved at Kleinfeld's in Manhattan since I bought my gown there too. If you go to their website there is a link to gown preservation. They restore entire gown (missing beads, pulled embroidery, tears, dirt, stains etc) and preserve it in a box that is same box used in Metropolitan Museum of Art to preserve their costumes.
The size of box depends on the size of your gown. Mine was huge! lol..
I paid about $500.00. Comes with white cotton gloves so you can handle dress, wrapped in acid free paper and instructions on how to refold it if you take it out of box . They recommend taking it out and checking it once a year.
My friend used an online service and they basically stuffed her large ballgown dress into a small box with a window. Destroyed her gown. Crushed the fabric so bad it could not be repaired.
I hope this helps!!