I just discovered recently that heavy tanks can be easily disabled using HE rounds. I guess most of you know it, but since I never saw it written on the forum and I only see complaints about the invincibility of German heavies, here it is ...
Just shoot near the gun : for panther you need to hit rather close to the gun, for Tiger and Ferdinand you need less precision.
Once the gun is disabled, you can try to destroy a track and then close up for the kill.
With this, you can attack frontall