Combat between vehicles and their crews works just like regular combat but with two additional modifiers.

Attack Modifiers

Unstable Platform: Any character on an unstable platform, including a moving vehicle, suffers a -2 penalty to any “fine” physical skills such as Fighting and Shooting. This applies to characters who are firing vehicular weapons as well. Note that the Steady Hands Edge eliminates this penalty.

Fast Target: A fast-moving vehicle is more difficult to hit, and subtracts 1 from any attacks directed at it for every full 10” of its speed. This is relative, so a vehicle heading directly toward a character doesn't get the modifier, nor does the modifier apply if the hero is shooting at a vehicle driving parallel to his own.

Savage Worlds Deluxe Edition p. 115