Hi Norintha,
Quick update on this — the feature you asked about is now live in DM_LimitedInventory V1.32!
You can now check specific storage boxes using three new script calls:
$gameContainers.getItemAmountFromContainer(containerId, itemId)
$gameContainers.getWeaponAmountFromContainer(containerId, weaponId)
$gameContainers.getArmorAmountFromContainer(containerId, armorId)
Each one returns the total count in that container, or 0 if it’s not there. They also work with DM_IndependentItems and will count unique instances correctly.
Thanks again for the suggestion 6 months ago — it made it into the plugin. Full details and examples are in the V1.32 help file.