I camped this spider for six hours and no pop. I tried again a couple days later, and after 2.5 hours, he popped in the middle of the room. -- This could just be incredibly bad luck, or it could be timers got reset after the latest update, or any other of a million possibilities. Who knows? Regardless, it was a grind of a camp for me.
Having read Sekhista's post, I was alittle concerned with pulling. Especially since these spiders do seem to have a big aggro radius and can, apparently, sense danger to their mates through walls.
In order to minimize the deaths, we started with the lone ember golem in the tunnel, outside Nightfang's spawn point. We literally sat on top of the golem and meleed him to death. Then, we entrapped the funnelweb spider that was nearby, and meleed him to death also. About that time, the roamer ember golem showed up, and, again, we meleed him to death. At that point, we set up midway between the wall and the door, facing the room where Nightfang spawns. Our ranger puller used Harmonious Arrow to pull out the leaper on the left of the doorway, closest to the door. We dragged the spider into the hall, and killed him - no adds. We repeated this singular pulling process for the other three leapers in the room, and the funnelweb spider that roams from the other side. We continued, occassionally pulling more spiders from the far room or more hateful fire elementals from the hallway to bide our time until Nightfang popped. We had zero deaths this way.
It wasn't all that exciting - more of a brutal grind kind of thing, but it got the job done and everyone in my group finished the Hunter Trophy for the Upper Floors with Nightfang's death.