im supprised you had so much of a fuss with this guy. by 55th he will be LB (well he was LB to me at 55th) and rather easy to chant down.
he did try to dark me 1 time, and did try to cast a few dots on me. all were resisted, and my resists are not ubber by any means. i would say my average resist across the line is between 50-80.. nothing lower then upper 40s and none of them are in the 100+ range without my resists songs up.
i used selo's, lev (from SS boots), DE mask (this did make him warmly to me) before i did the turn in. mind you i did not have Virt, or any other buff other then what i can produce myself with my gear (listed as what i had up).
as soon as i did my turn in and got the item and xp with the msg about his doppelganer(sp?) i ran out of there rather fast. he did not run after me as he was trying to cast. no biggy, first resist. i get back into range and hit him with cold dot, then start to pull him away from the camp so they dont bother me.
once out of the camp, i just chant him down. few resists, and took one DD for 400 points or so. nothing major. well under 1min, he was dead and i had my head for the turn in. very easy kill.
i could see being 50th and him being either DB or even con causing a bit of an issue. levels IMHO are what made the differance and why i resisted his spells so easy.
MR, PR, and DR buffs would be best thing you can get before trying to solo him again if you are under 55.
good luck.
p.s. you may wish to charm kite him down. charm something and bring it along with you. let this guy waist his mana on your pet then chant him as your pet beats on him.