hi there,
I preferred rockwool when I grew tomatoes and bananas. I had heard that coco slab was not as well-draining and that as it broke down little bits potentially could cause my tubing and emitters to clog- but I didn't use it so all I can do is pass on that rumor. It would probably be fine for an ebb-flow system.

With rockwool you set up your trays at a 2 percent angle so that the trays drain toward your reservoir. You would cut a slit in the wrap on that end so the water runs out. If you let the water build up you'd drawn your plants via serious root rot. I'm sure if you went to a hydro supplier someone there would be happy to instruct you, there are also instructions on the web. Good luck!