An easier way would be to get a level 5 alarm, by the Belle or the Slaughter house base and then when a tank comes, go GTA on it, i.e. get on it, pop the top hatch and kick out the people in it, then get to the garage fast and park it, because there will be Nazi RPGers runing around at Alarm 5. There are two tank classes, the tanks you see around town, and the Mammoth [C&C reference here] tank which has a 2 barrel main cannon. The smaller tank will can be stolen at anytime and alarm level, since their all around town and come out in Alarm 4, the Mammoth tanks only come out at Alarm 5, as I said before you will need to be very quick and close to a garage when attempting to collect them, since the tank will get killed after 2 RPG or tank cannon hits on both tanks.