Best strategy I used:
Use only red cars (small) with miniguns and emp.
When possible upgrade minigun and EMP, HP has the lowest priotity.
When minigun is updated enough then use pulse gun.
Max out pulse gun and EMP on all three cars.
When on the road cycle EMP on all three cars 3,2,1,3,2,1 .... etc.
EMP renders all enemy weapons useless and pulde gun damages ALL enemies which stand in its way, including rockets.
Very easy