I am terrible at Stonewall. Terrible.

Everybody is. I still don't see how victory is possible...I mean the amount of armor and counter armor you need just to compete with the enemy armor is ridiculous, AND you have to have tons of anti-infantry to deal with rangers/shrecks.
Although after that last match I think snipers and mortars are the way to go. If we play as Americans we can also use the Vickers MG armor pierce ability to deal with early light armor. Because we need so much armor it might almost be better for everyone to kind of pitch in. With 9 snipers and 9 mortars between three players I think you'll have an effective infantry-shield, especially with a few HMGs thrown in, so that all of us can spam M10 Tank Destroyers. If we get enough M10's (as Americans, I don't know what Wehr would use) we could overwhelm enemy armor before they have a chance to take advantage of our thin armor. 6-8 M10's will "oneshot" anything below a Panther.
Plenty of mortar and sniper fire to deal with everything else and give everybody a constant stream of MP, and I think it might be possible.
Alternatively we all skip the M10 and spam AT guns.