The best strategy I found against enemy tanks is to shoot at them from far away.
In this mission, I think the tanks are always on the move. Try finding a location where you can wait for them and surprise them. better be higher ground.
Another tactic is to be the driver and let your gunner do the shooting. When you're facing an enemy like this, the best thing to do is to drive pretty fast, and then change to 1st gear when there's a shell loaded. So every time the enemy fires you'll be moving fast making it hard for him to hit, and when your gunner is ready to fire, you move at a very low speed so he can actually hit something.
Good luck.