Couple things... having played my share of duergar/dwarf, human and giant pole specs I can tell you that a duergar doesn't get a whole ton of mileage out of polearm. A lot of your skills are size based, so duergars don't do them well. It still has it's uses, particularly entrap and cutoff (and the occasional chargeset) but overall you'll get more out of other specs w/o something in your package that plays off of what the duerg pole spec is good at. (IE, my dagger/avalanche/cutoff build)

Having also had trapping on a pole spec I'll tell you that your heavy polearm choices are *somewhat* limited. The only two -really- good ones are going to be difficult to get solo, and the two that are juuust heavy enough to make trapping fire are not exactly easy to get. Not insurmountable, by any means, but it just seemed like between disarm, weaponbreak etc. I never held on to my prize polearms long.

In general I am unimpressed with trapping. "Back when" it was a great legacy choice, now I can't think of many scenarios where I'd take it over some others. Even less so on a duergar, even if you do take fist of the titan.

Now, I think if you did exactly what you are talking about but went fire giant, and dropped fist in favor of something else... (Maybe Fires!)It's a viable build. As a duergar though... eh... I think your in for a dissapointment.