After fumbling around in the CS and looking for info about assigning ownership, it seems that you don't assign ownership in the window used to assign the unique ID and name to an item, but that you have to first place it in the world and then select it at which point a window with a different set of fields pops up. No wonder I didn't find the ownership field on the item's Unique ID window screen.

I'm making a small convenience mod for myself to place some items that I want Creeper to have for sale. I used a vanilla existing crate from the Containers tab, changed its Unique ID and saved/created the mod. For my next step, I placed the new container in Ghorak Manor next to Creeper. At this point, I double-clicked on the container so that I could continue with assigning ownership of the crate to Creeper. However, the fields related to ownership were greyed out and not able to be changed. Nor was the any NPC identified as the owner.

So where did I go wrong? The stuff I've read so far hasn't been very useful - I would have liked something that said do this, this and this, but the material assumes that you already know what you're doing. Am I supposed to use some other container instead of a crate? Is there a special class of container that is to be used if you want to be owned?

TIA for your help.

Edit: Found the extra data toggle. Can ownership of a crate (and its contents) be assigned to Creeper? I did not see "scamp_creeper" nor "Creeper" listed as an NPC in the drop down box of possible names to assign ownership of the crate I made.

Creeper is a creature, not an NPC. AFAIK, only NPCs can be assigned as owners.

In CS Creeper is a Daedra and I thought Daedra are treated as a NPC. Is a Daedra NPC, if I understood it correctly, an exception?

No, what Kir said. It does not matter how a creature looks (mesh/animation), a creature is not a npc and is managed in a different way by the engine regarding dialog filters, ownership, stats, factions and other things

@JH2011: I think you have 2 ways:
1. (simpler, may be incompatible with other mods changing creeper, but sometimes incompatibilities can be solved merging objects with TESTool); add items to the creature inventory in CS. Also, I'm not sure it will work if you bartered with creeper in a save already, may need deleting creeper saved data from save with e.g. Mash remover/tes3cmd/Enchanted Editor
2. (more complex if you can't script, compatible): add items by script
example:
a global script like this so you can avoid repeating scamp_creeper-> prefix a lot of times

begin jh2kAdd2CreeperScript; usage;; scamp_creeper->StartScript "jh2kAdd2CreeperScript"; add/replace objectid quantity as you see fitAdditem "balm amulet" 1Additem "pick_master" 2Additem "gold_001" 100stopscript jh2kAdd2CreeperScriptend

a local script to attach to a new invisible activator using e.g. the EditorMarker.nif mesh (e.g. a copy of Sound_Haunted00) placed in Creeper cell

begin jh2kAdd2CreeperActiScriptshort lastMonthif ( MenuMode )	returnendif; add items when month changesif ( Month == lastMonth )	returnendifset lastMonth to Monthscamp_creeper->StartScript "jh2kAdd2CreeperScript"end

Thanks for the feedback. I thought I was doing something wrong in the CS but obviously not.

@abot, thanks for the detailed suggestions. I'll stick with the first one then because this is a convenience mod for myself and the prior mod I had made for myself worked. I only got interested in the idea of using a container as the means to add inventory to Creeper because from what I have read conflicts with other mods are much less likely, not that I had noticed any with what I had done before. There is no danger about messing up a saved game because I'm starting a new game and was lining up which mods I wanted to use. And if I really need to, I can always use a "real" NPC merchant somewhere to carry the item(s). I used Creeper because Creeper was convenient, but there's no reason another merchant would not be a reasonable choice to carry the item(s) for sale.