For a couple of games I have, especially card games, I’ve taken to making box inserts. With the right materials for construction it’s actually pretty easy to do and cost a fraction of commercial products. One thing that stood out for me regarding the Arkham Horror LCG box though was its reduced box height. My Netrunner box was a snap to whip up, mostly as I just had to match the height of the box. It was already large enough to store cards on their side. The Arkham Horror box is much thinner, making it a little more of a challenge to get assembled.
I ended up creating a square box frame that would keep cards stored in two main compartments laying on their side. I cut the sides so that it was about 4mm wider than a sleeved card. Keep that in mind as some sleeves can be significantly larger than the dimensions of the cards, so you want to take that account in any measurements. You don’t want to accidentally make the frame too small, crimping and bending up your sleeved cards. Another point, don’t bother with putting a base section for your insert. With enough center support sections you can create a frame that will hold up fine in the box and as an added bonus have more space to work with. My frame slipped snugly into the box.
To support the box frame more, I separated each main card compartment into two using a single piece of foam board. I then carefully measured the two parallel, center boards and added another pair of sections so that each could hold a small number of cards, perpendicular in orientation to the cards in the main chambers. This center compartment was also kept hollow to store any odd little bits (more on that later). I ended up with a very sturdy foam insert with a well supported center to keep the box from buckling.
A couple of points on construction, you want to use foamcore board that is about 2-3 mm in thickness. You can use thicker pieces of foamboard however I find that after lining up the sides and multiple sheets used to make compartments, you end up losing a lot of space in the box, so thinner is better. I also used a hot glue gun to assemble the pieces together initially. It will pretty much set immediately and give you a pretty strong bond. I can then go back and add PVA (i.e. white, or Elmer’s) glue to all of the joints and set it aside to dry overnight. To add even more strength with thicker foamcore, you can use sections of toothpicks as dowels along with PVA glue.
For ease of getting cards in and out, I cut a notch into the foamcore supports used to separate the compartment sections. This was so I could easily get a finger in to pull out cards, yet didn’t remove too much material to weaken the section of the card. You could try cutting a round notch but practice a few trial cuts before you do. I found cutting round edges a little difficult to do with foamcore board over straight edges.
As to the actual dividers for different cards I used sections of foamcore cut shorter than the width of the cards. I also kept them loose and didn’t secure them to the walls of the insert. Right now I am unsure how many expansions I will be getting and how the card types will expand, so I wanted to maintain some flexibility. However I certainly wanted lots of sections to properly divide many of the cards, especially the encounter card sets. Cut with a tight fit in the box they actually have enough resistance to stand up by themselves (although over time the edges will get worn). Once I get a feel for how I want to separate my cards, I can secure them using a little PVA glue.
The center compartments I have for pre-made player decks. Currently I am using one to hold the encounter deck of the first scenario. Also you can make out the center section. I trimmed a few thin sections of foamboard and placed them in here. Some other scenarios can have many locations, so these thin sections can provide a better visual representation how locations are linked to each other. In the end I have a pretty nice little foam insert, with enough room to keep my tokens, investigator cards, and other bits secured in ziplock bags.
By not using a single sheet as a base (and instead just relying on the box itself) I was also able to reduce the overall profile of the box allowing the lid to sit securely on it. My rules and campaign books lay on top of the insert and the cross design gives it plenty of support. The box is certainly thicker but not so thick that the lid won’t keep secure.
You can certainly buy frame inserts that are great quality and reasonably priced. However with a little effort (I cranked mine out in an evening), you can make a similar insert at a fraction of the cost and be just as functional. Don’t be put off trying your own hand at making foamcore inserts. They actually are a pretty easy project to do.