Here are two Heavy Weapon Ork Buggies towing Big Gunz.
The Buggies have had their gunner replaced with a Flak weapon from a Flakwagon, whilst one of the Big Gunz is a conversion of a flak weapon from a Flakwagon).
The Buggies were given a black undercoat, dry-brushed with Tin Bitz and Chainmail, details were picked out in red and orks painted green.
The Gunz were given a white undercoat, the black elements (the tires) were painted first, before the rest of the model was painted red. They were then given a thinned chestnut ink wash.