It's hard, with all those mines and things. You realize that its only vulnerable spot is that little square in its back, right? So you have to keep circling behind it to shoot at that spot. The beam is good, but don't get too close, or it will pop mines out under you. Rockets probably help a lot; I didn't use them.
Try not to let the mines build up so much you have no room to manoeuvre, but as long as there aren't too many, you can ignore them and keep circling the tank. The mines fade away after a while anyway.
And luck helps. Sometimes the tank drops lots of mines, sometimes not so many; sometimes it shoots straight at you, and sometimes it gets sort of stuck against a wall and leaves its Achilles' tail exposed for a few long seconds. Keep trying, and eventually you'll get it.