the only times i have died with my zerker barb is when there is conviction council + the amp dmg and maybe a might aura council.
I made the runeword "Flickering Flame" for my merc - which gives him and myself a massive amount of fire res (and thus even with a conviction aura you still have 50-60+ fire res depending on your roll). Might sound like an overkill for merc, but he never dies. Neither do I. He needs life leech from the weapon though in this case - in the beginning I was using Reapers until I was able to switch to an eBotd.
Reapers is ok, but not ideal as it adds a bit of cold damage and occasionally the merc would pop 1-2 bodies. If you want to optimize your build he needs no cold damage at all.
The second thing is: you simply need super quick clear speed - which can almost only be accomplished with Grief in your main hand. My trav runs are 30-45seconds, and it is a breeze. Attack is your best defense in this case.