An Oak armour case flatpack can be made at a workbench (Steel framed bench or better) in the workshop of a player-owned house. Like when making the normal Oak armour case, this requires 46 Construction, uses 3 oak planks, and gives 180 experience. The flatpack can then be used on a armour case hotspot in a Costume room, either in building mode or not. This requires no Construction level and gives no experience.
The cost of making and selling a Oak armour case flatpack from scratch gives a profit of: -1,285
After completing the hard Fremennik Tasks, they can also be traded to Advisor Ghrim in exchange for 84 coins being added to your kingdom's coffers in Miscellania. See Flatpack: Miscellania reselling for details.
See Armour case for a list of armours that can be stored.