Failed every time (due to lag/LDs every time but one).
I'm getting very frustrated with it, so I thought a thread where people who've done it successfully could post their tips/strategies on how to do it (prefereably with a normal Co5-type group) might be helpful for all the poor sods like me

From a healers point of view the problem is people not being targetable for cure-poison/heals/rezz down in the ditch. People go down there, get poisoned, can't be healed, die, a healer has to stop healing the group to run right up front to rezz, gets poisoned him/herself, gets LOP from rezzing, other healer can't keep up with keeping the group alive & needs to spam group-heals, Shade pops ... group half-dead ... healers OOP ... healers get agro ... & bye-bye.
Apparently the melee types HAVE to go down there tho to stop Crom AoEing, or so I'm told at least.