There are Orks who have looted Imperial weaponry. Not only can they use Space Marine weapons they can also borrow the transport.
A Looted Rhino is an Imperial Rhino armoured personnel carrier that has been looted from a previous battlefield by Ork Lootas and is now used as a transport for their WAAAGH!
When I was constructing the Ork Battlewagon I decided against using the included turret. This is how the Battlewagon looks with the included turret, though I decided not to use it with the Battlewagon, made it a little too tall for my liking.
So I decided to have a go at seeing how it looked on my Ork Looted Rhino. There was an Imperial Predator turret ring in the Rhino kit and this nicely fitted the Ork Battlewagon turret, as well as fitting the Rhino hatch area.
Very much like an Imperial Predator.
The Battlewagon had additional smaller turrets, so I decided to try them out as well and see how they looked.
I gave all the turrets a white undercoat.
Here is the smaller turret.
Here is a cupola with a Heavy Bolter.
Here is the larger undercoated turret.
I started my Ork Looted Rhino many years ago, and the process I used is outlined on my workbench feature on the Looted Rhino.