I don't deal with vehicles very much, so I'm not sure this will work, but when I have issues with humanskins or inventory models, I copy and past the .def file from an existing model into the one I'm having issues with. If it works with the .def from an existing mode then at least I know that's where the problem lies.
Docs.google.com
This is the .def file, I looked but I saw nothing wrong but if you want to
look go ahead.
I don't deal with vehicles very much, so I'm not sure this will work, but when I have issues with humanskins or inventory models, I copy and past the .def file from an existing model into the one I'm having issues with. If it works with the .def from an existing mode then at least I know that's where the problem lies.
Making changes where necessary of course.