I wish they made that kind spawn at the gypsy/brigand camps. And I also wish they could be engraved with the wooden engraving tool (not a container it informs you, oh really??)
It is surprisingly difficult to find info on where the covered barrel spawns. I couldn't find anything on the Stratics rares/semi rares forums.
For any enterprising thief, all I could find on another site, is that the covered barrels spawn in room north of Bone Magi in Deceit (lv1&2)
UOAM coordinates (1st lvl): x5193, y587
UOAM coordinates (2nd lvl): x5302, y593
-Skylark