If you see another player target one of your own 2moons gold vehicles, kill him. Vehicles go down faster to players than other vehicles. Prioritize vehicles. If you see an enemy vehicle, go after it, even if it means enemy players will get free hits on you. Vehicles can't repair themselves -- and Mechanical Repair Kits are simply too low-level to make any difference -- so each hit you make on a siege vehicle is worth more than a hit on a player who will be healed or rezz soon after.