The milestone quest requires you to destroy player structures when in a vehicle. This can be any vehicle found on the island, so boats, cars and trucks will all work.

You can get this by simply driving around the island in a car and looking for player structures left over from build battles to ram until they are destroyed but this is time consuming and risky as the enemy players will hear you coming from a distance and you will be a sitting duck in the car.

A faster way to get this quest line done is to jump into a team rumble game. If you are lucky the later stages of the game will be near water. If so you can use a boat to fire rockets into the enemy teams forts. There is always a lot of building in team rumble so you will have plenty of targets to hit.

If the final circle is on land and there are no boats available a car will work, especially on wooden builds but it is less effective than using the boat rockets.

This quest also includes destroying your own structures or structures built by your team. So if you are looking for a way to grind this you can find a quiet part of the map and build wooden structures when ram them with a vehicle or use the boat rockets.