Tank used FV215B 183
If you penn soft targets with the Hesh rounds you get alot of internal dmg. The FV4005 or the 183 are very good for this mission. Try and stay alive so you can get the artys at the end, that helps alot and can save you that round with just one shoot. You could ofc do this in an arty but the rounds tend to be to fast and you get of to few shoots. Its actually pretty rare to dmg internal models with arty. Another way to go is to try and set someone on fire.
Best of luck to you all