Use your first tank to shoot it like 3 times then use mechanized company artillery.
You can try siege it with an at gun earlier, but thats pretty costly(map control) and risky(obers can come and just rek your at gun) I would only recommend this if the Flak base is in a crucial spot of you know he can't respond to you doing this
The flak base also won't switch targets ever unless something dies or moves away so you can run in infantry if its shooting a tank pretty safely
