take "fairly simple" to mean "it's pretty easy when you get the hang of it."
anyway, here's some more detail that hopefully will help:
don't ignore the destroyers' high resistance to fire..don't just add another SH or SF ele to your group to compensate - turn the fire magic to zero...Destroyers are anet's way of reminding you that there are 3 other elements.
Actually, i don't bring ele's at all..armor ignoring damage is the way to go. I have my own ranger spread conditions - poison arrow, screaming shot + signet of infection, and Finish Him for my offensive conditions; you're all weaklings and throw dirt to hamper melee destroyers. For heroes i run MM (close combat minions for body-blocking and death nova), SS and a WoH Monk..Mhenlo's got LoD covered and if you're doing this right you shouldn't need so many party heals that you need to run a LoD hero. Lina, Lo Sha, and Zho round out the group. Notice there really isn't a whole lot of aoe, here...aoe is great for the first wave, but heavy degen works best i found for the final five waves.
Since i don't use a lot of aoe, the first wave can (but not usually) get a little hairy if you wait back by the dragon..this wave i usually creep up one side, kill a few, run to other side - the minions will stick around and hold the fort for a time while i take my party to the other gate and repeat the process.
second wave, i usually flag hench in between both doorways..usually what happens is the destroyers of hordes on the side i'm closest to will agro while inside the tunnel and stand there barraging the wall while i take care of the compassions up close. Then, when there's no compassions around, i peak around the corner and apply degen. If you wait up by the dragon and fail to kill the hordes fast enough you can find yourself getting barraged from 8 directions, which isn't very fun with heroes/hench standing on top of each other.
for the rest of the waves i stay up by the dragon
third wave is really easy..if you have trouble with it, then you already died on the second wave so don't worry about it.
fourth wave, look for the melee mobs to come out and usually your minions will corner block them on the rise up to the dragon and prevent them from coming up to your casters..use your weakness and blind causing skills to help them tank and that's about it
fifth wave..this is why you brought Zho. The lvl 28 ele's here are the only real danger..they pop up at regular intervals in three spots close to the dragon..they arrive one at a time, and there are four..keep an eye out for them until you've got the pattern down because you need to target these as soon as they pop-up to make sure Zho targets them with her interrupts. The last thing you want is two of them firing aoe at your hench..they will die, quickly.
sixth wave is easy..each boss should be dead or very near so before the next one shows up and none of the bosses has any kind of back-up.
once you "get it," it should be fairly simple, with the only point of concern being the occasional miscue on your own part...over time you'll probably find yourself getting more cloths of the brotherhood than you will destroyer cores.
