Can't seem to figure how to correctly apply Texture Atlas or Trim Sheet ontop of other texture.

Hey, so I have exported some of the Fortnite assets for educational purposes. (Trying to learn UE4 Sequencer). And I want to populate the environment with a few Fortnite buildings/assets to learn a part of the pipeline and make the environment match to the characters I am animating in Sequencer.

However, Epic seems to have used a weird texture set up that does not make sense to me. Probably because it’s an optimised texture call method.

So, current issue:

I have one Mesh. It’s a modular Cabin Wall. It is an FBX with only one Material ID. (I am not sure if the export to PSKX made it lose the Material ID’s set originally).
There are 3 UV Channels (0 to 2). However, 0 and 2 have the same main bulk texture of the wall. So I can’t just use a texCord node. Channel 1 is empty according to the UV viewer in UE4.
There is a Material called “Cabin_Wall” which is clearly for the majority of the wall. I setup that material like normal.

As you can see above, I have tried to do a float to blend the two materials together. But of course that did not work as planned.
I have also tried texCord’s, Lerp’s, UE4 Material Layers and tried a few blends like Decals.

Without trim:

There is then a “Cabin_Trim” material. Which seems to be a modular texture atlas or trim sheet for all the Cabin modular meshes.
However, I cannot seem to find a way to have the trim texture ontop of the wall texture without the trim texture tiling all the way across the wall. I can clearly see that in channel 0, the trim fits the window frame as it should. But then the main wall is the rest of the texture atlas.

With Trim:

Is there any way around this? Or do I need to go back and set Material ID’s in 3Ds Max? (I would rather not as there are probably 100’s of meshes that would need it doing to them for different meshes that use different trim sheets).

Note: I do not think I am allowed to send these assets due to that being re-distribution. As mentioned, using these assets is purely educational and for fan-made content.


Bump would certainly like some insight on this if possible