Defender 18 FPIU:
Zip: addon > Grab "defendpack" and put it in OpenIV > GTAV > mods > update > x64 > dlcpacks
Then go to OpenIV > GTAV > mods > update > update.rpf > common
find "dlclist.xml" right click > edit, go down the list and put
<Item>dlcpacks:/defendpack/</Item> above /Paths> then press save.
ELS: Grab "18defendfpui.xml" from the addon and put it in GTAV >ELS > pack_default
After doing this you can spawn your cars from the trainer, it's in the added vehicle list
Repeat the process for the other cars and it should work 😄
Some vehicles have the procedure in their readme files, make sure to read it all the time