Ulm vs Wraithes isn't easy, tin men lose all advantages vs ethereal undead ...
What about trying Holy Pyre (Evo4, Fire 2) ?
A Smith with either a Fire helmet or using 1 gem can cast it, it should destroy any undead easily (AP 7 attack x3 vs Undead).
On the minus side precision isn't good ...
Else there's the Just Man Cross Xbow (Cons2 Fire 1), you can make many of'em, but surely Eye of Aiming will be necessary to have a decent hit rate.