I printed 2 of the other auto trash bag hooks I found here on Thingiverse. Both of them broke. I don't know if it is a limitation of my printer or material but I decided to design my own using the strength of the orientation of the printing process to enhance the hooks capability. I'd suggest printing each part in the orientation that I have in the OpenSCAD screenshots.

Neither of the other hooks properly fit my vehicle which is the reason that I decided to go with links. You can print as many or a few as needed to fit your vehicle and they conform to the seat.

I had some of the commercial wire hooks but found the wind could blow the grocery bag out of the hooks. This is the reason for the tight fit of the bag hook. Mine won't blow out

Note: You will also need 1/8 inch rod stock of some sort to make the pins for all the links.