Building structures and truck take damage if you’re shooting while in/on/near them. I have a link to my Xbox game clip where the hunting outpost gets destroyed in seconds when I’m shooting from it, on Reddit someone mentioned that the bullet casings do the damage but as you will see in my clip, the casings eject to the right and the wall to my left gets destroyed along with the hunting outpost.
Every structure that you can build, turrets, grenade pillbox, sandbag, crafting tables, everything, they all take damage when you shoot in/on/near them.
Here is the link to my game clip on Xbox: https://www.xbox.com/play/media/LQ9G4D44