Guide taken from me on TA.
This Trophy is easiest obtained using a tank, The easiest way to get a tank is to find the challenge "Tank it 2 the MAX." This challenge can be found on the bottom right corner of the map and is represented by an Orange skull, near the Scrap Metal building.
This rampage starts you with a tank, Hold down the Square button to keep the chain going drive around blowing everything up until the counter hits 99. May take a few retries with the timer