Of course it's out dated but that was not the question, The question was about how to fix a texture issue. My bad advice would be to watch a fillman86 video to get even more confused unless you actually understand the edits he makes.
The mod itself is extremely outdated, by SEVERAL years and would require a crap ton of work just to get it somewhat functioning properly again. Best option is to just delete the mod and use the base game trailers since they fulfil the role this mod once did. the last update the ar16b trailer addon mod received was way back in 2021, roughly 3 years ago. The game itself has gone through a considerable number of changes, something that would need to be fixed beyond just the textures would be how the Trailers in this mod couples to tow hitches and goosenecks since those have drastically changed via code.
