I have WOYWW ATC's going back to the 4th Birthday celebrations, and I had envelopes holding them safe everywhere.
I finally got around to getting them safely put away, using Storage Sheets bought from Amazon.
I've yet to decorate the covers!
These are the specific Trading Card pockets,but they come in a wide variety of pocket sizes,intended as Currency/postcard/photo storage amongst many others.
The 4 pocket square ones are ideal for storing the cards that sometimes come with an ATC.
This is a screen shot from the Amazon page in the link,so you can see what's available.
They come in batches of 10 pages, so the trading card ones will store 90 ATC's.
I also find the 3 pocket one great for storing large tags in, and larger ATC's too.
All of this years in their pockets now.
Another great use for these pockets is storing spare die cuts.
The wide range of pocket sizes lets you store all sorts of die cuts- just in case you ever remember you have them!
A third use for them is storing unmounted rubber stamps, especially the bare rubber ones.
No matter how large, or small your stamps, there are pockets that will fit them.
Hope this will be useful/helpful in your storage issues!