To unlock the White Gold trophy in Far Cry New Dawn, you will need to capture one of the game's 10 Outposts. Once you have captured an Outpost, stand on a street nearby and patiently wait for an Ethanol tanker to pass by. The spawns are random, but you shouldn't have to wait for too long.
When you see an Ethanol tanker driving by, shoot the driver, defeat any enemies that are in the vicinity, get in the truck and drive it to the nearby Outpost.
You can, of course, go out looking for an Ethanol tanker to steal, but they are highly explosive, making this much easier if your close to an Outpost already.