Here's the Airfix Opel Blitz and PaK 40 from an MPC boxing.
The Blitz has some acetate windows plus I masked and applied multiple layers of primer to define the bottoms of the window flaps. The kit piece just had them blend into the rest of the bed cover, I suppose so the part would release from the mold. Paint is Tamiya sand over Vallejo Panzer gray, revealed by the AK chipping fluid process.
The Pak had the muzzle brake drilled out and the channel in the mount that the gun slides on in recoil whittled out. Paint is Model Master.
Both are weathered with pastels.