Towable lift good idea, they weren't around when I got a bucket, so this style lift wasn't an option.
The drawback I see to something like this would be backing into postion might be a problem.
You mentioned hills, trying to pull or back a towed piece of equipment up or down a hill is definately going to be problem, especially with a small truck, like a p/up.
Working with towed equipment works best on flat level ground with good traction for the tow vehicle.
Just thought I would throw this in, to give you something more to ponder on.
As far as using a knuckle boom to lift, Eric is right, some are equipped with material handlers for top boom, others are equipped with winches on the lower boom for lifting. As general rule, knuckles should not be used the same as a crane.
Larry