I have a small box now, but soon have to do something similar for the expansion. I'm also interested how You did those, what seems to be a foamcore based divider. Tell us.
It's indeed foamcore (although it went by the name of "advertising board" at the local hardware store). The thickness of the foamcore is 5 mm.
The measurements of the box itself are 29cm x 29cm x 7cm. The height of the foamcore is 6 cm as the decks are easier to get out if they are a little higher than the walls, and also the box still closes tighly even if you put the rulebook on top of the cards.
The one long strip on the middle is the full 29cm long and the walls between the decks are 10 cm long, you'll need 8 of those. The deck slots are 4.6cm wide, give or take 1mm. Both strips that separate the kingdom boards from the decks are 18.5cm long and the short strip near the middle is 3cm long. There is still a good 2cm between the kingdom board and the wall so they are easy to get out from the box too, although it can't be seen from this angle. For glueing I used a standard PVA glue.
As for the work itself I first cut and glued the long edge (29cm strip and 5x10cm strips), then the short edge (18.5cm strip and 3x10cm strips) and finally the other 18.5cm strip together with 3cm strip. This way there was still room for changes if any errors were found.
It took a little over an hour to do the whole box. Hope this helps.
As for the 12 decks, atleast there is enough room for expansions. Atleast 6 will be needed for each race (Empire, Orcs, Chaos, Dwarfs and the eventual release of Helfs and Delfs), plus there is room for extra cards, which won't make it to ready decks.
This is great. I copied your measurements (except I made the walls a little shorter (5cm) and added more dividers. I put a small piece of foam board beneath the left side of the capital boards so I could easily get them out of the box.
My cards were bugging me, having to look through a few card boxes I had them in. This is exactly what I needed. Thanks again!