IIRC, the Matty is heavily armored, even the rear of the tank has rather thick armor. You might want to disable it's tracks and then get to a position from where you can get a straight (dont know if SF recognises angled shots or not) shot to it's rear.
Ow and try to hit it to the engine deck area thingy, it's abit sloped so you should be able to knock it out from that spot.