Engine swap problems.

I've swapped a modified ETK 2.4L engine into a barstow, and it's all running super well.
However I have one problem, the textures are completely broken. In the .zip folder for my mod, I have the engine, transmission, and exhaust .jbeam files from the ETK, the .dae from the ETK, and the .cs files for the barstow and I-series respectively named materials.cs and materials_etk.cs. For some reason the textures on the engine, trans and exhaust are broken ("no material" texture appears). I've spent ages trying to figure it out but I can't seem to find the problem.

I have gotten it all to work before aswell, but it seems after I got the exhaust in the textures broke, though I'm not sure if that is the problem. A screenshot of the files is attached.

 

The only materials file name allowed is "materials.cs", so you have to either combine the files into one or put the wrongly named file to a subfolder and fix the name.

 

Ahh, thanks! Should I put the barstow or ETK materials into a subfolder?
Edit: I have put the barstow materials into a subfolder named "barstow", and now the only problem is the interior textures, which still do not work.