Mana potting is usually no big deal in duels. People just have really high faster cast rate and faster hit rate %'s. Makes for a lot of spam and a full belt ='s a shit load of mana.
I'd also recommend getting at least some block with Whitstans (sp) or some shit. May come in handy when that barb tries to get that kb on you.
Having even a small revive / skeletal army will help keep the mobs away from you. Spam decrep or amp damage and let the skeles / revives rape with you.
My necro Schayde was a summoner. I took out peope just by teleporting on them wiht JUST SKELETONS. Course I used beast and bo too.