I've gone ahead and added a Waterwell NPC to Outpost, but he's just standing there waving. No-one can interact with him and pull up his trades. Is there something I'm doing wrong?

        {
          "Id": "34d9d5e1-0e8b-4776-b936-d8ffedf93062",
          "PrefabName": "assets/prefabs/npc/waterwell/waterwell_shopkeeper.prefab",
          "Position": {
            "x": 2.72632027,
            "y": 0.27718544,
            "z": -2.31930661
          },
          "RotationAngles": {
            "x": 0.0,
            "y": 132.9711,
            "z": 0.0
          },
          "OnTerrain": true
        },​

You didn't do anything wrong. The NPC shopkeepers require an additional vending machine to be spawned right next go them (an invisible one) which the plugin doesn't currently do. I'm not sure if its possible for you to work around this issue for the water well shopkeepers, but in other cases you can simply spawn the invisible vending machine on them and it would usually work, though the angle and position has to be right.