My suggestion: if you don't want to scare away these guys, decrease the number of nobz in the battlewagon and drob the Nob Bikers all together. Nob Bikers are terrifying, even in small numbers. Replace them with boyz. And replace the biker boss with a Big Mek with a
KFF. That should give them a challenge without you completely wrecking them

Others might say something different, this is just
IMHO