Yeah, the slabs are sitting in the trays and the wrappers are just hanging over the edges to keep high humidity and light out of the rootzone. I'm currently setting up an automated watering system, but once it's in place I'm going to seal the wrappers to the trays with tape.
I didn't like leaving the wrapper on and cutting slits in the bottom. They would either clog up or be too big and the water wouldn't have a chance to get wicked very well. After I harvested and opened them up, a lot of the rockwool looked like it had never been touched by water let alone roots.