If you are not committed to using perlite, you might want to consider sharp sand - the type used in making concrete. It drains very well, but stays moist enough - not having to be watered more than twice a day, even under hot windy conditions. It also anchors the cuttings well as it packs tighter than perlite, and you won't have to deal with the dust associated with perlite. I bought a large bag - I believe it was 4 cu. ft. - of perlite, and just trying to wet down a couple of quarts results in clouds of very fine dust that can cause lung problems. We had a pile of sharp sand delivered, and use it for most of our cuttings. It has worked very well.