i use notepad + to edit the " loot.xml " in my Config file, found at :\Program Files (x86)\Steam\steamapps\common\7 Days To Die\Data\Config your install may be different. the containers all have the same basic definition, like this for player storage
<lootcontainer id="1" name="playerStorage" count="0" size="12,10" sound_open="UseActions/open_chest" sound_close="UseActions/close_chest" loot_quality_template="qualBaseTemplate">
as you see, i've edited mine to 12 columns by 10 rows. it will only change newly placed containers in a save, will not change existing containers. and if i forgot something, someone will come along and correct me