Had this one turned on and was not really going for it then got a patrol and spotter medal in the same game which also happened to be the first game in the string of 10. Jumped into the Lorr T8 arty and farmed confederate medals. Simpy remember which tanks you have shot and getting damage to 6 tanks is super easy. Confed farming in arty is a very easy way to get epic medals for missions.
Decided to have a crack at this with the Grille 15. Have only done 2 battles, but already have 11.2k of the 30k required in the bank. Whacking an FV4005 for over 1500hp with a HE shell (and resulting fire) was a high 5 moment! Very confident that this tank will do the needed damage. I did think about the JPE but the flexibility of the turret, and much better overall mobility swung it to the Grille. Any tank you do well in would work, but I think this mission suits the stand off, huge alpha approach (you don't care about XP). You only need 4 pens to get the average damage required in the Grille. Fighting just behind HTs gives you plenty of HP to farm, and lets you move forward or back as you need to. You can also retreat behind your armour and pop out to shoot enemy hts on reload. Always understand where your next fallback fire position is and leave early, better to miss 1 potential shot and stay alive than to take 1 more and die as you are over-run. Pushing forward early in the game helps make sure you have space to fall back on. Look for spots with potential shots into 2 contested areas right from the start. The more your gun sings the easier it is. Don't expect to get this by bush camping and extreme long distance sniping. If you have not shot in 1 minute then you need to move to keep that gun in action.
Damage is needed to 4 different tanks. High RoF, accurate and high pen on a mobile platform is preferred. I used E50 with 88mm gun, but I would also strongly consider using arty as well. Its very easy to switch targets once you have damaged a tank, and you can shoot at pretty much the whole map if you need to. Usually the stock guns have a faster aim time and RoF so they are the ones to use to get the maximum number of shots out. Possibly a Type 4/5 with HE rounds would work but they can be caught out if you need other tanks.