green,  built a wooden frame for the back and covered it with canvas. When  it came time to shoot, they either towed the truck from the front,  or pushed it from behind with another vehicle, depending on the  angle of the shot. A giveaway to this is a shot taken underneath the  truck, when Indy (Chris) is dragging behind the truck, it can be  seen that the truck has no axle connecting the front and back  wheels.