I've gone absolutely min-max on my play through - Blackwall as full on S&B Tank and 3 mages (all with barrier and reduced threat).
I stack the mages in one spot, they keep barrier up 95% of the time. Two have freeze, they all have traits to increase mana regen when not moving (Ice magic tree). Throw down some flame walls, mines, lots of freeze, shock and burning and nothing has come close to stopping me unless it is a much higher level. Once I got Dorian (my 3rd mage since I don't agree with Vivienne on some political issues) I get out of most fights without anyone on my party taking any actual damage.
Once I get blizzard, I think I should be able to play the rest of the game on autopilot :P