I made a thing! Here's the Thingiverse.com description and the link. I can't get pictures to work... but totally click the link.

https://www.thingiverse.com/thing:2811655

My wife and I love the Arkham Horror LCG put out by Fantasy Flight Games. I've lost track of our decks a couple of times, forcing us to restart a campaign. I decided to make an insert for the core box that will allow me to track everything. As you can see, the insert has space for six decks and a ton of tokens. One of the boxes is large enough to hold a handful of miniatures. We're using some from the Mansions of Madness 2nd Edition board game from the same company. The way I'm currently using it is to hold the 4 player decks and the upcoming scenario. The black bag has the current scenario's doom tokens. I keep everything else in a proper card storage box and binder. You can also see the Lola Hayes Role Selector (https://www.thingiverse.com/thing:2750956) on top of the doom token bag.

The insert is modular and designed to be taken out of the box and used when playing. The deck holders can be used to keep your deck from sliding around while playing. I should note that this works great with both FFG and Dragon Shield sleeves. The item marked as "discard" can be used either as a little vertical discard pile or for the Agenda and Act decks in AH.

Due to the boxes being the exact same size, this will also work with the Android Netrunner Revised Core and the Legend of the Five Rings (L5R) Core. I checked and it'll hold all the tokens for both.

You'll need to print...
6x Card Holders
2x Small Boxes
2x Medium Boxes
2x Discards
1x Miniatures Holder

I printed everything at a 0.20mm layer height. It took awhile to print all the parts, but it's totally worth it.