I suggest to do it with some strong armor lower tier tanks like Matilda, T18, AMX 38/40, S35, AT2 etc. Already got 2/3 not too hard in Matilda. Look only for matches when you are top tier. Since most of them is quite slow because of stronger armor don't wait too long.
When both teams became thined out go for flag by some backdoors. Biggest problem is your teammates who migh steal your cap points.