There are Orks who have looted Imperial weaponry. Not only can they use Space Marine weapons they can also borrow the transport. I wrote about my Ork Looted Rhino and where I was in progressing it and then added the tracks.
When I was constructing the Ork Battlewagon I decided against using the included turret. So I decided to have a go at seeing how it and some smaller turrets looked on my Ork Looted Rhino. Having painted the turrets, I gave the Heavy Bolter Cupola a wash of Agrax Earthshade.
This wasn’t quite the effect I wanted, in order to match the existing Rhino body. Close, but not close enough.