No, you are right, I thought maybe there was rockwool in there but nah you dont need it.
I just copied the commercial aero cloners with what I had available. The res is an old esky (cooler) with holes drilled in the top so the 2 inch netpots drop in snug. There is a good tutorial here to give you some ideas. Mine is basically a simpler version -
https://www.rollitup.org/t/harvest-a-pound-every-three-weeks.116859/page-499
Then on the inside I just used pvc to make a frame and a small aquarium pump. I have tried all the sprayers they sell at the hardware store and found the mini sprinklers to be the best and I only need 4 so the pressure stays high. These are the onese I use -
https://www.bunnings.com.au/pope-micro-mini-spinner-5-pack_p3120466
After much experimentation, 15 mins on / 30 mins off gives me roots nubs in 4 - 5 days and those roots in the picture above in about 10 days in summer. Winter it takes a few more days due to the cooler weather.
I use straight tap water and then dose with about 5ml of H2O2 every few days to keep it sterile until there are a good spray of roots, then hit them with a light veg nute mix to get them moving as I do zero veg SoGs so they go straight from cloner to flower.
I only change the solution and wash everything once the clones are gone to flower, ready for the next batch. I generally toss out a third of the rooted clones I have as I always take extra and just choose the ones with the biggest roots.
Happy building!