Installation: 
- Make sure you have the appropriate gameconfig to support multiple add-on vehicles: https://www.gta5-mods.com/misc/gta-5-gameconfig-300-cars 

- Make a new folder 'ssc_yosemite' via OpenIV in: update\x64\dlcpacks 
- Drop the dlc.rpf contained in the 'ssc_yosemite' folder into the ssc_yosemite folder you made
- Edit the dlclist.xml file in OpenIV: update\update.rpf\common\data 
- Add the new line: 
    <Item>dlcpacks:\ssc_yosemite\</Item>

Spawn the vehicle with a trainer using the model name: yosemite6str