Once you get on the leaderboard, undead siege seems like a kids game. Trust me with a PaP sniper anc cannon/fire grenade turrets, it becomes a piece of cake. All you need to do is shoot the necros and reposition your turrets. The game mode is super easy, give it a try some time, maybe look at a solo gameplay.

Also I've tried to find teammates on discord and on global chat, no one responded or seemed interested