3 Pulleys is the way to go.
I found some good pics online and some QJers gave some good info as well.

I have my rig set up so I can either hang from single point ( over a limb) or from 2 points (between 2 trees). I beleive Azalea gave the tip to keep the pack closer to one tree so you don't get that sagging effect over a long distance.

Sometimes you can get some twisting issues around the pulley that hooks to pack. I fixed that problem by running the line thru a foot of clear 3/8 plastic tubing that sits right above it.

I also switched to this item for my ropes, even the haul rope. I wrapped my 2 hanging lines and haul rope/ pulley rig around 1/2" pvc pipe and use it to pull this thin but incredibly strong line.

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This line doesn't absorb water, has little stretch and really lightens your bear hanging kit.