I was thinking recently of a res/root seperator idea too, and honestly I bet a setup similar to a dark room vent rig would work well.

Such as 3 seperate sheets of plastic that are ALMOST as wide as the grow tub, setup like this (top view)

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This way the roots wouldnt become hopelessly entangled in the millions of little holes, or screen (if that idea was used), and it makes a LONG way to travel for the roots that do find their way around the first edge. Make sense?

Oh, and if it was a recirculating system, you'd want the water to come into the section furthest from the drain too I think.