Hi Brain, Rockwool isn't the favorite medium but I have tryied it on 2 grows and for clones. I think it would be your best choice right now. Just don't keep it too wet. Perilite doesn't hold anything up. Your choice of growing medium should be hydrotron clay pepples or lava rock. Lava rock can be gotten just about anywhere, you know the kind for gas grills. Just break it up some more with hammer and wash it good. forget the perilite and use all rock and plant the plug of rockwool it there. The rockwool will give you a few days to get it together. Are you going to hand water or use a drip pump? The system will work just needs tweeking.Tell us more of your grow setup and plans and more help will come.