Make barrels spawn ONLY in containers

[kmiles1990 5]

How do I make barrels spawn ONLY in containers? 

 

Right now I have this.

<type name="Barrel_Red">
        <nominal>500</nominal>
        <lifetime>3888000</lifetime>
        <restock>0</restock>
        <min>10</min>
        <quantmin>-1</quantmin>
        <quantmax>-1</quantmax>
        <cost>100</cost>
        <flags count_in_cargo="0" count_in_hoarder="0" count_in_map="1" count_in_player="0" crafted="0" deloot="0"/>
        <category name="containers"/>
        <tag name="floor" />
        <usage name="Village" />
    </type>

But it spawns the barrels EVERYWHERE. It's very annoying.

[Malotru 2]

<type name="Barrel_Red">
        <nominal>500</nominal>
        <lifetime>3888000</lifetime>
        <restock>0</restock>
        <min>10</min>
        <quantmin>-1</quantmin>
        <quantmax>-1</quantmax>
        <cost>100</cost>
        <flags count_in_cargo="0" count_in_hoarder="0" count_in_map="1" count_in_player="0" crafted="0" deloot="0"/>
        <category name="containers"/>   <!-- Catégorie d'apparition de butin - (liens vers mapgroupproto.xml)  -->
        <usage name="Industrial"/>	    <!-- Zone d'apparition Industriel -->
    </type>