[andrewas]

Umber hulks are among the most annoying creature in BG2, but i havent got to them in IWD yet. The following is therefore based on general principles:

Protect from confusion. Chaotic commands and suchlike.

And then the general fighter buff spells:

Recitation and Prayer (If you cast these with the umber hulks in range your effecive bonus is +6)

Haste. Add another 1 to that bonus and double your attacks.

Open up with a fireball barrage and procede as you see fit.