Squid Bolts and Brimstone Flasks tend to be better than Mass Destruction against zoos; Mass Destruction does have the advantage of destroying walls though.

Necro is incredibly powerful if you have enough Necro Resist and/or healing and/or curse removal to handle the debuffs. Pact of Fleeting Life is great healing itself if you can melee at all. Tenebrous Rift can kill 90% of a zoo with one or two casts.

For extra steel, you can take Clockwork Knight and/or Perception to cause monsters to randomly drop extra metal; Perception alone usually gives me 20 steel (and at least that much Iron) by floor 8 or so. And some cheese. And some pants.

...search function appears to have died. There was another Dredmor post that's probably past the necro time limit by now, but there should be some more discussion there (a lot of which has been obsoleted by patches and expansion packs, but eh :P )