Good deal, another use for an age old design. Chicken waterers using this method have been around longer than me.......and that is a long time! Also the same as a lot of current dog and cat waterers. That should work good and you could make them just about any size you want.
Seedlings are left in the rockwool when moved to either hydroponics or soil planting. The plant roots grow throughout the rockwool, and will emerge when transplanted.