I found these guys in Hobbyco, a large Sydney retailer and thought five bucks for a hummer-sweet. They fit perfectly with 20mm but in a pinch can be used for 15mm as well, great sci fi utility vehicles.

A quick paint an weather and bingo, ready to play plus they are metal as well. They had some other makes as well including a Mercedes 4WD hopefully they also do a Land Rover and Hilux.