This storage solution was first featured in a BGG thread, but I have received approval to post it on this site so that other players get to see it. Hopefully, this inspires more people to store their cards in unique ways and share them with the community. See the original thread for links to printing templates for you to replicate this storage solution!

This is a storage solution that nicely keeps the encounter cards in the deluxe expansion boxes (I store all player cards standing up in the core box.)
The Inserts
You have the option of creating the inserts from A4 or A3; I’ve been using the A4 version. To get either pdf template, please check the original article, as it requires a BGG account to access it.
Print the Cutout template, cut it and apply it to your choice of insert paper. Cut and fold them.
Tape if they need help to keep their shape (depends on the paper type). Put them in the box.
Now it´s ready to store cards!

Storing Strategy
The sagas will easily go two in one box, so you have some options for what to do with the extra space of four empty boxes. All the POD scenarios will fit to be put with the cycles in releasing order as I’ve done, or you can keep them by themselves. I don’t know what would be preferable with Nightmare expansions since I don’t have any of those.
I have put the Core Set quests together with the Shadows of Mirkwood cycle in the On the Doorstep box (as shown in the picture). The other spare saga boxes I use for fan-made expansions, like the awesome The First Age expansions.
The more cards you cram into a box, the more they’ll stand up and the higher the lid will sit. For now, I keep the rule sheets in the deluxe boxes, just on top of the cards, and it does add to the height. I prefer no more than 400 cards per box; else, it stands up too high. Note that the slope at which you store the cards is quite shallow if you don’t have as many cards in the box, allowing the lid to close easier. The more cards you add to the box, the taller you will have to stand the cards up. That means that at full capacity, the cards will be standing up nearly vertical, making it more difficult to close the box and put the belt on. By widening the belt, you can allow it to slide over the closed box easier and keep everything nicely in place.
Belt

One big factor for me to develop this solution was that I not only wanted to use the deluxe boxes, but I wanted them to be standing up! Therefore I made these belts:
Print the Belt.PDF (see the original thread for the pdf link) on A4, laminate, cut, fold, and tape two of them together. It’s hard to get them in the right size/tightness, so only tape one end, then fold around the box and tape the other end. I also made a belt for the core box. Same procedure; just use three belt pieces.
I suppose you could use tape instead of laminate to enhance the paper; regular paper won’t hold.
There’s probably a way to get a more invisible belt, like with a strong dark sewing thread, or maybe there’s a solution with something that can be unbuttoned to make the putting on and taking off easier.
Please note that the belt should not be too tight. The lid of the box is kept up by the cards inside, meaning that if you press down too hard, you could end up damaging the cards. You can try using some tape to find the perfect length of the belt for your box, before fastening the two ends permanently.
Thanks
Once again, a big thanks to GeckoTH for his contributions of DIY material to this great game. As you can see in the picture, I’m using his dividers (can be found here: GeckoTH horizontal, GeckoTH vertical, and my continuation of them here: Jonker horizontal, Jonker vertical).
Please share or/and improve this idea! (There´s a way to make this type of insert with the original inserts, but I don´t want to cut mine, so I leave that to someone else.)

Once again, a big thank-you to Jonker for sharing his storage solution on the blog. If you have a unique storage solution that you want to be featured on the blog’s Storage Hub, feel free to reach out to me via the contact page or by sending me your solution through social media. I’d be happy to feature it as long as it is different enough from all other solutions on the hub so far.