Well if you remember the lock on the tanks is 30 seconds. What I try to do is wait until a tank is built, then kill whoever paid for it. Its good to do with a buggy/humm vee, either by running them over or shooting them. When you see the 3 green arrows over the tank, abandon your vehicle for the tank. Either cause chaos in the base or return to your base for repairs (when they get onto the fact you are not the enemy).I got an apache using this method on walls, they got my stolen buggy but I think I got the better deal!