I have managed to make what it resembles to be Seatbelts in Gmod, these dont serve any porpose and are only for looks.
I make them out of a 16 Bone, Strap model with PAC3 and then I give it the most realistic material in the list. (currently using some plastic Texture)
If you want me to make one for you, just ask in a comment. Provide what colour and what type of seatbelt I will make and any extra stuff you want. Your name will be above the picture if you asked.
**Constructive Criticism would be appreciated! **
Here are some of the Seatbelts I have made in PAC3: