On some body types, the Backless Extravaganza and Anarchic [Colour] Outfit camp clothes have clipping issues, and the character's legs and butt will clip through the pants during movement. This mod fixes that.

Affected body types:

Human Masc
Human Masc Strong
Human Femme Strong
Githyanki Masc
Githyanki Femme
Dwarven Femme
Gnome Masc
Dragonborn Femme
Half-Orc Femme

Installation:

I highly recommend using BG3 Mod Manager to install your mods, if that's an option for your operating system.

For detailed installation instructions for BG3MM or manual installation, see the BG3 wiki's Installing Mods guide.

Manual installation: Copy the code below into your modsettings.lsx file according to the BG3 Wiki's Installing Mods guide.
            <node id="ModuleShortDesc">
                <attribute id="Folder" value="PantsReinforcement" type="LSString" />
                <attribute id="MD5" value="" type="LSString" />
                <attribute id="Name" value="BacklessOutfitPantsReinforcement" type="LSString" />
                <attribute id="UUID" value="5b5cf34c-ebe7-4fd4-aaa2-b0be828ea209" type="FixedString" />
                <attribute id="Version64" value="36028797018963968" type="int64" />
            </node>

How does this mod work? Will it apply to modded outfits/other vanilla outfits/characters with custom bodies?

This mod edits the visual resource definition for the pants resource used by these vanilla outfits, and tells it to make the "Thighs" section of the base body model invisible. (The body types that aren't included in this mod have this set up for these pants already.) The vanilla outfits are made by referencing both the definition of the pants resource and the definition of the shirt resource, which are separate. Many outfits are made through different combinations of visual resources, so if a vanilla or modded outfit calls on the same pants resource that I edited, the fixes from this mod will carry over.

If you use a custom body replacer, this mod will hide the "Thighs" section of that body just fine when you equip these outfits. Hiding the butt and thighs is all this mod can do, though - the actual shape of the clothes themselves depends on the mesh, so unless your body mod includes a replacement for the vanilla meshes, the clothes will still follow the vanilla body shape and there will likely be clipping in other areas.

Other notes:
Thanks to lokelani for additional screenshots.