Now you've got me curious. Any idea how well these ultra pro clamshell boxes would fit? Ultra Pro 2-Piece 150 Count Clear Card Storage Box https://www.amazon.com/dp/B0002TT3LG/ref=cm_sw_r_cp_apa_Px0MzbSSYXS1V I use those for all of my commander decks. It is annoying having to jam them all in my backpack though. Also, the fit of these? http://www.ultimateguard.com/en/boxes-cases/boulder-deck-case/deck-case-100.html

I use Ultra Pro 2-Piece 150 Count Clear Card Storage Boxes for my decks. https://www.amazon.com/Ultra-Pro-81147-2-Piece-Storage/dp/B0002TT3LG/

I keep them on a bookshelf for display and easy retrieval.

I use an Ultimate Guard Arkhive 400+ to bring 4 decks with me when I'm playing at my LGS or at my friends' houses. https://www.amazon.com/Ultimate-Guard-Arkhive-XenoSkin-Black/dp/B01M25T2AK/ (4 of the Ultra Pro 2-Piece 150 Count Clear Card Storage Boxes fit in it perfectly) I throw it in my backpack with a playmat, dice bag, and box of tokens.

If I'm traveling and need to bring more than 4 decks I can throw up to 12 decks into my Stanley organizer. https://i.imgur.com/838s7ZG.jpg (I usually remove the compartments to fit the deck boxes in it.)

That RIDGID organizer that u/DanteBeleren recommended looks awesome too. I may have to check into it since it looks like they can snap together for even more storage.

Ultra Pro 81147 2-Piece 150 Count Clear Card Storage Box https://www.amazon.com/dp/B0002TT3LG/ref=cm_sw_r_cp_api_i_d2dREbJ7TW1TT

These are what I use. Can fit 4 perfectly into a boulder and they can hold a double sleeved deck plus a few tokens easily.