When I've set up aeroponic pots, I fill the net pot half-way with growrocks, and put the 1.5 inch rockwool cube on the rocks, and then fill rocks around the cube, packed tight, and then covering the top of the cube.
You want a lot of roots growing out the sides of the netpots as well as the bottom, so that will anchor your plant when it's heavy with buds.
HTH
