I'm like Anne...I use the water bottles also, but I use more of the medium sized ones so that I can place them closer together. I use window screening (which comes pre-cut and on cardboard rolls) to place between the bottles and soil. I used to use peanuts but they are a mess to clean up if you want to make any changes and I used to use the very hard Styrofoam blocks that came with TV's but they are hard to cut to fit into round pots.
Oh...and
Bobdoss!