This is an ambush and are going to come to you. Study the landscape. Tanks cannot cross mountains, and your rocket launcher must be defended. Look for places that are difficult to attack. Place the rocket launcher where there are mountains on three sides. Put a tank on the fourth side and do not move it. Invisible tanks still behave like normal tanks. They cannot move after they attack. However, you can only see them when you have a unit next to them. Send out one or two units to "scout" for tanks. If you find some, attack them with the rocket launcher or the other tanks. Your enemy will run out of tanks before you do. Do not extend too far from your "base".